GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2060

Network Working Group M. Crispin Request for Comments: 2060 University of Washington Obsoletes: 1730 December 1996 Category: Standards Track

          INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1)
 allows a client to access and manipulate electronic mail messages on
 a server.  IMAP4rev1 permits manipulation of remote message folders,
 called "mailboxes", in a way that is functionally equivalent to local
 mailboxes.  IMAP4rev1 also provides the capability for an offline
 client to resynchronize with the server (see also [IMAP-DISC]).
 IMAP4rev1 includes operations for creating, deleting, and renaming
 mailboxes; checking for new messages; permanently removing messages;
 setting and clearing flags; [RFC-822] and [MIME-IMB] parsing;
 searching; and selective fetching of message attributes, texts, and
 portions thereof.  Messages in IMAP4rev1 are accessed by the use of
 numbers.  These numbers are either message sequence numbers or unique
 identifiers.
 IMAP4rev1 supports a single server.  A mechanism for accessing
 configuration information to support multiple IMAP4rev1 servers is
 discussed in [ACAP].
 IMAP4rev1 does not specify a means of posting mail; this function is
 handled by a mail transfer protocol such as [SMTP].
 IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and
 unpublished IMAP2bis protocols.  In the course of the evolution of
 IMAP4rev1, some aspects in the earlier protocol have become obsolete.
 Obsolete commands, responses, and data formats which an IMAP4rev1
 implementation may encounter when used with an earlier implementation
 are described in [IMAP-OBSOLETE].

Crispin Standards Track [Page 1] RFC 2060 IMAP4rev1 December 1996

 Other compatibility issues with IMAP2bis, the most common variant of
 the earlier protocol, are discussed in [IMAP-COMPAT].  A full
 discussion of compatibility issues with rare (and presumed extinct)
 variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is
 primarily of historical interest.

Table of Contents

IMAP4rev1 Protocol Specification ……………………………. 4 1. How to Read This Document …………………………… 4 1.1. Organization of This Document ……………………….. 4 1.2. Conventions Used in This Document ……………………. 4 2. Protocol Overview ………………………………….. 5 2.1. Link Level ………………………………………… 5 2.2. Commands and Responses ……………………………… 6 2.2.1. Client Protocol Sender and Server Protocol Receiver ……. 6 2.2.2. Server Protocol Sender and Client Protocol Receiver ……. 7 2.3. Message Attributes …………………………………. 7 2.3.1. Message Numbers ……………………………………. 7 2.3.1.1. Unique Identifier (UID) Message Attribute ……… 7 2.3.1.2. Message Sequence Number Message Attribute ……… 9 2.3.2. Flags Message Attribute ……………………………… 9 2.3.3. Internal Date Message Attribute ……………………… 10 2.3.4. [RFC-822] Size Message Attribute …………………….. 11 2.3.5. Envelope Structure Message Attribute …………………. 11 2.3.6. Body Structure Message Attribute …………………….. 11 2.4. Message Texts ……………………………………… 11 3. State and Flow Diagram ……………………………… 11 3.1. Non-Authenticated State …………………………….. 11 3.2. Authenticated State ………………………………… 11 3.3. Selected State …………………………………….. 12 3.4. Logout State ………………………………………. 12 4. Data Formats ………………………………………. 12 4.1. Atom ……………………………………………… 13 4.2. Number ……………………………………………. 13 4.3. String …………………………………………….. 13 4.3.1. 8-bit and Binary Strings ……………………………. 13 4.4. Parenthesized List …………………………………. 14 4.5. NIL ………………………………………………. 14 5. Operational Considerations ………………………….. 14 5.1. Mailbox Naming …………………………………….. 14 5.1.1. Mailbox Hierarchy Naming ……………………………. 14 5.1.2. Mailbox Namespace Naming Convention ………………….. 14 5.1.3. Mailbox International Naming Convention ………………. 15 5.2. Mailbox Size and Message Status Updates ………………. 16 5.3. Response when no Command in Progress …………………. 16 5.4. Autologout Timer …………………………………… 16 5.5. Multiple Commands in Progress ……………………….. 17

Crispin Standards Track [Page 2] RFC 2060 IMAP4rev1 December 1996

6. Client Commands ……………………………………. 17 6.1. Client Commands - Any State …………………………. 18 6.1.1. CAPABILITY Command …………………………………. 18 6.1.2. NOOP Command ………………………………………. 19 6.1.3. LOGOUT Command …………………………………….. 20 6.2. Client Commands - Non-Authenticated State …………….. 20 6.2.1. AUTHENTICATE Command ……………………………….. 21 6.2.2. LOGIN Command ……………………………………… 22 6.3. Client Commands - Authenticated State ………………… 22 6.3.1. SELECT Command …………………………………….. 23 6.3.2. EXAMINE Command ……………………………………. 24 6.3.3. CREATE Command …………………………………….. 25 6.3.4. DELETE Command …………………………………….. 26 6.3.5. RENAME Command …………………………………….. 27 6.3.6. SUBSCRIBE Command ………………………………….. 29 6.3.7. UNSUBSCRIBE Command ………………………………… 30 6.3.8. LIST Command ………………………………………. 30 6.3.9. LSUB Command ………………………………………. 32 6.3.10. STATUS Command …………………………………….. 33 6.3.11. APPEND Command …………………………………….. 34 6.4. Client Commands - Selected State …………………….. 35 6.4.1. CHECK Command ……………………………………… 36 6.4.2. CLOSE Command ……………………………………… 36 6.4.3. EXPUNGE Command ……………………………………. 37 6.4.4. SEARCH Command …………………………………….. 37 6.4.5. FETCH Command ……………………………………… 41 6.4.6. STORE Command ……………………………………… 45 6.4.7. COPY Command ………………………………………. 46 6.4.8. UID Command ……………………………………….. 47 6.5. Client Commands - Experimental/Expansion ……………… 48 6.5.1. X<atom> Command ……………………………………. 48 7. Server Responses …………………………………… 48 7.1. Server Responses - Status Responses ………………….. 49 7.1.1. OK Response ……………………………………….. 51 7.1.2. NO Response ……………………………………….. 51 7.1.3. BAD Response ………………………………………. 52 7.1.4. PREAUTH Response …………………………………… 52 7.1.5. BYE Response ………………………………………. 52 7.2. Server Responses - Server and Mailbox Status ………….. 53 7.2.1. CAPABILITY Response ………………………………… 53 7.2.2. LIST Response ………………………………………. 54 7.2.3. LSUB Response ……………………………………… 55 7.2.4 STATUS Response ……………………………………. 55 7.2.5. SEARCH Response ……………………………………. 55 7.2.6. FLAGS Response …………………………………….. 56 7.3. Server Responses - Mailbox Size ……………………… 56 7.3.1. EXISTS Response ……………………………………. 56 7.3.2. RECENT Response ……………………………………. 57

Crispin Standards Track [Page 3] RFC 2060 IMAP4rev1 December 1996

7.4. Server Responses - Message Status ……………………. 57 7.4.1. EXPUNGE Response …………………………………… 57 7.4.2. FETCH Response …………………………………….. 58 7.5. Server Responses - Command Continuation Request ……….. 63 8. Sample IMAP4rev1 connection …………………………. 63 9. Formal Syntax ……………………………………… 64 10. Author's Note ……………………………………… 74 11. Security Considerations …………………………….. 74 12. Author's Address …………………………………… 75 Appendices ……………………………………………….. 76 A. References ………………………………………… 76 B. Changes from RFC 1730 ………………………………. 77 C. Key Word Index …………………………………….. 79

IMAP4rev1 Protocol Specification

1. How to Read This Document

1.1. Organization of This Document

 This document is written from the point of view of the implementor of
 an IMAP4rev1 client or server.  Beyond the protocol overview in
 section 2, it is not optimized for someone trying to understand the
 operation of the protocol.  The material in sections 3 through 5
 provides the general context and definitions with which IMAP4rev1
 operates.
 Sections 6, 7, and 9 describe the IMAP commands, responses, and
 syntax, respectively.  The relationships among these are such that it
 is almost impossible to understand any of them separately.  In
 particular, do not attempt to deduce command syntax from the command
 section alone; instead refer to the Formal Syntax section.

1.2. Conventions Used in This Document

 In examples, "C:" and "S:" indicate lines sent by the client and
 server respectively.
 The following terms are used in this document to signify the
 requirements of this specification.
 1) MUST, or the adjective REQUIRED, means that the definition is
    an absolute requirement of the specification.
 2) MUST NOT that the definition is an absolute prohibition of the
    specification.

Crispin Standards Track [Page 4] RFC 2060 IMAP4rev1 December 1996

 3) SHOULD means that there may exist valid reasons in particular
    circumstances to ignore a particular item, but the full
    implications MUST be understood and carefully weighed before
    choosing a different course.
 4) SHOULD NOT means that there may exist valid reasons in
    particular circumstances when the particular behavior is
    acceptable or even useful, but the full implications SHOULD be
    understood and the case carefully weighed before implementing
    any behavior described with this label.
 5) MAY, or the adjective OPTIONAL, means that an item is truly
    optional.  One vendor may choose to include the item because a
    particular marketplace requires it or because the vendor feels
    that it enhances the product while another vendor may omit the
    same item.  An implementation which does not include a
    particular option MUST be prepared to interoperate with another
    implementation which does include the option.
    "Can" is used instead of "may" when referring to a possible
    circumstance or situation, as opposed to an optional facility of
    the protocol.
    "User" is used to refer to a human user, whereas "client" refers
    to the software being run by the user.
    "Connection" refers to the entire sequence of client/server
    interaction from the initial establishment of the network
    connection until its termination.  "Session" refers to the
    sequence of client/server interaction from the time that a mailbox
    is selected (SELECT or EXAMINE command) until the time that
    selection ends (SELECT or EXAMINE of another mailbox, CLOSE
    command, or connection termination).
     Characters are 7-bit US-ASCII unless otherwise specified.  Other
     character sets are indicated using a "CHARSET", as described in
     [MIME-IMT] and defined in [CHARSET].  CHARSETs have important
     additional semantics in addition to defining character set; refer
     to these documents for more detail.

2. Protocol Overview

2.1. Link Level

 The IMAP4rev1 protocol assumes a reliable data stream such as
 provided by TCP.  When TCP is used, an IMAP4rev1 server listens on
 port 143.

Crispin Standards Track [Page 5] RFC 2060 IMAP4rev1 December 1996

2.2. Commands and Responses

 An IMAP4rev1 connection consists of the establishment of a
 client/server network connection, an initial greeting from the
 server, and client/server interactions.  These client/server
 interactions consist of a client command, server data, and a server
 completion result response.
 All interactions transmitted by client and server are in the form of
 lines; that is, strings that end with a CRLF.  The protocol receiver
 of an IMAP4rev1 client or server is either reading a line, or is
 reading a sequence of octets with a known count followed by a line.

2.2.1. Client Protocol Sender and Server Protocol Receiver

 The client command begins an operation.  Each client command is
 prefixed with an identifier (typically a short alphanumeric string,
 e.g. A0001, A0002, etc.) called a "tag".  A different tag is
 generated by the client for each command.
 There are two cases in which a line from the client does not
 represent a complete command.  In one case, a command argument is
 quoted with an octet count (see the description of literal in String
 under Data Formats); in the other case, the command arguments require
 server feedback (see the AUTHENTICATE command).  In either case, the
 server sends a command continuation request response if it is ready
 for the octets (if appropriate) and the remainder of the command.
 This response is prefixed with the token "+".
    Note: If, instead, the server detected an error in the command, it
    sends a BAD completion response with tag matching the command (as
    described below) to reject the command and prevent the client from
    sending any more of the command.
    It is also possible for the server to send a completion response
    for some other command (if multiple commands are in progress), or
    untagged data.  In either case, the command continuation request
    is still pending; the client takes the appropriate action for the
    response, and reads another response from the server.  In all
    cases, the client MUST send a complete command (including
    receiving all command continuation request responses and command
    continuations for the command) before initiating a new command.
 The protocol receiver of an IMAP4rev1 server reads a command line
 from the client, parses the command and its arguments, and transmits
 server data and a server command completion result response.

Crispin Standards Track [Page 6] RFC 2060 IMAP4rev1 December 1996

2.2.2. Server Protocol Sender and Client Protocol Receiver

 Data transmitted by the server to the client and status responses
 that do not indicate command completion are prefixed with the token
 "*", and are called untagged responses.
 Server data MAY be sent as a result of a client command, or MAY be
 sent unilaterally by the server.  There is no syntactic difference
 between server data that resulted from a specific command and server
 data that were sent unilaterally.
 The server completion result response indicates the success or
 failure of the operation.  It is tagged with the same tag as the
 client command which began the operation.  Thus, if more than one
 command is in progress, the tag in a server completion response
 identifies the command to which the response applies.  There are
 three possible server completion responses: OK (indicating success),
 NO (indicating failure), or BAD (indicating protocol error such as
 unrecognized command or command syntax error).
 The protocol receiver of an IMAP4rev1 client reads a response line
 from the server.  It then takes action on the response based upon the
 first token of the response, which can be a tag, a "*", or a "+".
 A client MUST be prepared to accept any server response at all times.
 This includes server data that was not requested.  Server data SHOULD
 be recorded, so that the client can reference its recorded copy
 rather than sending a command to the server to request the data.  In
 the case of certain server data, the data MUST be recorded.
 This topic is discussed in greater detail in the Server Responses
 section.

2.3. Message Attributes

 In addition to message text, each message has several attributes
 associated with it.  These attributes may be retrieved individually
 or in conjunction with other attributes or message texts.

2.3.1. Message Numbers

 Messages in IMAP4rev1 are accessed by one of two numbers; the unique
 identifier and the message sequence number.

2.3.1.1. Unique Identifier (UID) Message Attribute

 A 32-bit value assigned to each message, which when used with the
 unique identifier validity value (see below) forms a 64-bit value

Crispin Standards Track [Page 7] RFC 2060 IMAP4rev1 December 1996

 that is permanently guaranteed not to refer to any other message in
 the mailbox.  Unique identifiers are assigned in a strictly ascending
 fashion in the mailbox; as each message is added to the mailbox it is
 assigned a higher UID than the message(s) which were added
 previously.
 Unlike message sequence numbers, unique identifiers are not
 necessarily contiguous.  Unique identifiers also persist across
 sessions.  This permits a client to resynchronize its state from a
 previous session with the server (e.g. disconnected or offline access
 clients); this is discussed further in [IMAP-DISC].
 Associated with every mailbox is a unique identifier validity value,
 which is sent in an UIDVALIDITY response code in an OK untagged
 response at mailbox selection time.  If unique identifiers from an
 earlier session fail to persist to this session, the unique
 identifier validity value MUST be greater than the one used in the
 earlier session.
    Note: Unique identifiers MUST be strictly ascending in the mailbox
    at all times.  If the physical message store is re-ordered by a
    non-IMAP agent, this requires that the unique identifiers in the
    mailbox be regenerated, since the former unique identifers are no
    longer strictly ascending as a result of the re-ordering.  Another
    instance in which unique identifiers are regenerated is if the
    message store has no mechanism to store unique identifiers.
    Although this specification recognizes that this may be
    unavoidable in certain server environments, it STRONGLY ENCOURAGES
    message store implementation techniques that avoid this problem.
    Another cause of non-persistance is if the mailbox is deleted and
    a new mailbox with the same name is created at a later date, Since
    the name is the same, a client may not know that this is a new
    mailbox unless the unique identifier validity is different.  A
    good value to use for the unique identifier validity value is a
    32-bit representation of the creation date/time of the mailbox.
    It is alright to use a constant such as 1, but only if it
    guaranteed that unique identifiers will never be reused, even in
    the case of a mailbox being deleted (or renamed) and a new mailbox
    by the same name created at some future time.
 The unique identifier of a message MUST NOT change during the
 session, and SHOULD NOT change between sessions.  However, if it is
 not possible to preserve the unique identifier of a message in a
 subsequent session, each subsequent session MUST have a new unique
 identifier validity value that is larger than any that was used
 previously.

Crispin Standards Track [Page 8] RFC 2060 IMAP4rev1 December 1996

2.3.1.2. Message Sequence Number Message Attribute

 A relative position from 1 to the number of messages in the mailbox.
 This position MUST be ordered by ascending unique identifier.  As
 each new message is added, it is assigned a message sequence number
 that is 1 higher than the number of messages in the mailbox before
 that new message was added.
 Message sequence numbers can be reassigned during the session.  For
 example, when a message is permanently removed (expunged) from the
 mailbox, the message sequence number for all subsequent messages is
 decremented.  Similarly, a new message can be assigned a message
 sequence number that was once held by some other message prior to an
 expunge.
 In addition to accessing messages by relative position in the
 mailbox, message sequence numbers can be used in mathematical
 calculations.  For example, if an untagged "EXISTS 11" is received,
 and previously an untagged "8 EXISTS" was received, three new
 messages have arrived with message sequence numbers of 9, 10, and 11.
 Another example; if message 287 in a 523 message mailbox has UID
 12345, there are exactly 286 messages which have lesser UIDs and 236
 messages which have greater UIDs.

2.3.2. Flags Message Attribute

 A list of zero or more named tokens associated with the message.  A
 flag is set by its addition to this list, and is cleared by its
 removal.  There are two types of flags in IMAP4rev1.  A flag of
 either type may be permanent or session-only.
 A system flag is a flag name that is pre-defined in this
 specification.  All system flags begin with "\".  Certain system
 flags (\Deleted and \Seen) have special semantics described
 elsewhere.  The currently-defined system flags are:
      \Seen       Message has been read
      \Answered   Message has been answered
      \Flagged    Message is "flagged" for urgent/special attention
      \Deleted    Message is "deleted" for removal by later EXPUNGE
      \Draft      Message has not completed composition (marked as a
                  draft).

Crispin Standards Track [Page 9] RFC 2060 IMAP4rev1 December 1996

      \Recent     Message is "recently" arrived in this mailbox.  This
                  session is the first session to have been notified
                  about this message; subsequent sessions will not see
                  \Recent set for this message.  This flag can not be
                  altered by the client.
                  If it is not possible to determine whether or not
                  this session is the first session to be notified
                  about a message, then that message SHOULD be
                  considered recent.
                  If multiple connections have the same mailbox
                  selected simultaneously, it is undefined which of
                  these connections will see newly-arrives messages
                  with \Recent set and which will see it without
                  \Recent set.
    A keyword is defined by the server implementation.  Keywords do
    not begin with "\".  Servers MAY permit the client to define new
    keywords in the mailbox (see the description of the
    PERMANENTFLAGS response code for more information).
    A flag may be permanent or session-only on a per-flag basis.
    Permanent flags are those which the client can add or remove
    from the message flags permanently; that is, subsequent sessions
    will see any change in permanent flags.  Changes to session
    flags are valid only in that session.
    Note: The \Recent system flag is a special case of a
    session flag.  \Recent can not be used as an argument in a
    STORE command, and thus can not be changed at all.

2.3.3. Internal Date Message Attribute

 The internal date and time of the message on the server.  This is not
 the date and time in the [RFC-822] header, but rather a date and time
 which reflects when the message was received.  In the case of
 messages delivered via [SMTP], this SHOULD be the date and time of
 final delivery of the message as defined by [SMTP].  In the case of
 messages delivered by the IMAP4rev1 COPY command, this SHOULD be the
 internal date and time of the source message.  In the case of
 messages delivered by the IMAP4rev1 APPEND command, this SHOULD be
 the date and time as specified in the APPEND command description.
 All other cases are implementation defined.

Crispin Standards Track [Page 10] RFC 2060 IMAP4rev1 December 1996

2.3.4. [RFC-822] Size Message Attribute

 The number of octets in the message, as expressed in [RFC-822]
 format.

2.3.5. Envelope Structure Message Attribute

 A parsed representation of the [RFC-822] envelope information (not to
 be confused with an [SMTP] envelope) of the message.

2.3.6. Body Structure Message Attribute

 A parsed representation of the [MIME-IMB] body structure information
 of the message.

2.4. Message Texts

 In addition to being able to fetch the full [RFC-822] text of a
 message, IMAP4rev1 permits the fetching of portions of the full
 message text.  Specifically, it is possible to fetch the [RFC-822]
 message header, [RFC-822] message body, a [MIME-IMB] body part, or a
 [MIME-IMB] header.

3. State and Flow Diagram

 An IMAP4rev1 server is in one of four states.  Most commands are
 valid in only certain states.  It is a protocol error for the client
 to attempt a command while the command is in an inappropriate state.
 In this case, a server will respond with a BAD or NO (depending upon
 server implementation) command completion result.

3.1. Non-Authenticated State

 In non-authenticated state, the client MUST supply authentication
 credentials before most commands will be permitted.  This state is
 entered when a connection starts unless the connection has been pre-
 authenticated.

3.2. Authenticated State

 In authenticated state, the client is authenticated and MUST select a
 mailbox to access before commands that affect messages will be
 permitted.  This state is entered when a pre-authenticated connection
 starts, when acceptable authentication credentials have been
 provided, or after an error in selecting a mailbox.

Crispin Standards Track [Page 11] RFC 2060 IMAP4rev1 December 1996

3.3. Selected State

 In selected state, a mailbox has been selected to access.  This state
 is entered when a mailbox has been successfully selected.

3.4. Logout State

 In logout state, the connection is being terminated, and the server
 will close the connection.  This state can be entered as a result of
 a client request or by unilateral server decision.
          +--------------------------------------+
          |initial connection and server greeting|
          +--------------------------------------+
                    || (1)       || (2)        || (3)
                    VV           ||            ||
          +-----------------+    ||            ||
          |non-authenticated|    ||            ||
          +-----------------+    ||            ||
           || (7)   || (4)       ||            ||
           ||       VV           VV            ||
           ||     +----------------+           ||
           ||     | authenticated  |<=++       ||
           ||     +----------------+  ||       ||
           ||       || (7)   || (5)   || (6)   ||
           ||       ||       VV       ||       ||
           ||       ||    +--------+  ||       ||
           ||       ||    |selected|==++       ||
           ||       ||    +--------+           ||
           ||       ||       || (7)            ||
           VV       VV       VV                VV
          +--------------------------------------+
          |     logout and close connection      |
          +--------------------------------------+
       (1) connection without pre-authentication (OK greeting)
       (2) pre-authenticated connection (PREAUTH greeting)
       (3) rejected connection (BYE greeting)
       (4) successful LOGIN or AUTHENTICATE command
       (5) successful SELECT or EXAMINE command
       (6) CLOSE command, or failed SELECT or EXAMINE command
       (7) LOGOUT command, server shutdown, or connection closed

4. Data Formats

 IMAP4rev1 uses textual commands and responses.  Data in IMAP4rev1 can
 be in one of several forms: atom, number, string, parenthesized list,
 or NIL.

Crispin Standards Track [Page 12] RFC 2060 IMAP4rev1 December 1996

4.1. Atom

 An atom consists of one or more non-special characters.

4.2. Number

 A number consists of one or more digit characters, and represents a
 numeric value.

4.3. String

 A string is in one of two forms: literal and quoted string.  The
 literal form is the general form of string.  The quoted string form
 is an alternative that avoids the overhead of processing a literal at
 the cost of limitations of characters that can be used in a quoted
 string.
 A literal is a sequence of zero or more octets (including CR and LF),
 prefix-quoted with an octet count in the form of an open brace ("{"),
 the number of octets, close brace ("}"), and CRLF.  In the case of
 literals transmitted from server to client, the CRLF is immediately
 followed by the octet data.  In the case of literals transmitted from
 client to server, the client MUST wait to receive a command
 continuation request (described later in this document) before
 sending the octet data (and the remainder of the command).
 A quoted string is a sequence of zero or more 7-bit characters,
 excluding CR and LF, with double quote (<">) characters at each end.
 The empty string is represented as either "" (a quoted string with
 zero characters between double quotes) or as {0} followed by CRLF (a
 literal with an octet count of 0).
    Note: Even if the octet count is 0, a client transmitting a
    literal MUST wait to receive a command continuation request.

4.3.1. 8-bit and Binary Strings

 8-bit textual and binary mail is supported through the use of a
 [MIME-IMB] content transfer encoding.  IMAP4rev1 implementations MAY
 transmit 8-bit or multi-octet characters in literals, but SHOULD do
 so only when the [CHARSET] is identified.

Crispin Standards Track [Page 13] RFC 2060 IMAP4rev1 December 1996

 Although a BINARY body encoding is defined, unencoded binary strings
 are not permitted.  A "binary string" is any string with NUL
 characters.  Implementations MUST encode binary data into a textual
 form such as BASE64 before transmitting the data.  A string with an
 excessive amount of CTL characters MAY also be considered to be
 binary.

4.4. Parenthesized List

 Data structures are represented as a "parenthesized list"; a sequence
 of data items, delimited by space, and bounded at each end by
 parentheses.  A parenthesized list can contain other parenthesized
 lists, using multiple levels of parentheses to indicate nesting.
 The empty list is represented as () -- a parenthesized list with no
 members.

4.5. NIL

 The special atom "NIL" represents the non-existence of a particular
 data item that is represented as a string or parenthesized list, as
 distinct from the empty string "" or the empty parenthesized list ().

5. Operational Considerations

5.1. Mailbox Naming

 The interpretation of mailbox names is implementation-dependent.
 However, the case-insensitive mailbox name INBOX is a special name
 reserved to mean "the primary mailbox for this user on this server".

5.1.1. Mailbox Hierarchy Naming

 If it is desired to export hierarchical mailbox names, mailbox names
 MUST be left-to-right hierarchical using a single character to
 separate levels of hierarchy.  The same hierarchy separator character
 is used for all levels of hierarchy within a single name.

5.1.2. Mailbox Namespace Naming Convention

 By convention, the first hierarchical element of any mailbox name
 which begins with "#" identifies the "namespace" of the remainder of
 the name.  This makes it possible to disambiguate between different
 types of mailbox stores, each of which have their own namespaces.

Crispin Standards Track [Page 14] RFC 2060 IMAP4rev1 December 1996

    For example, implementations which offer access to USENET
    newsgroups MAY use the "#news" namespace to partition the USENET
    newsgroup namespace from that of other mailboxes.  Thus, the
    comp.mail.misc newsgroup would have an mailbox name of
    "#news.comp.mail.misc", and the name "comp.mail.misc" could refer
    to a different object (e.g. a user's private mailbox).

5.1.3. Mailbox International Naming Convention

 By convention, international mailbox names are specified using a
 modified version of the UTF-7 encoding described in [UTF-7].  The
 purpose of these modifications is to correct the following problems
 with UTF-7:
    1) UTF-7 uses the "+" character for shifting; this conflicts with
       the common use of "+" in mailbox names, in particular USENET
       newsgroup names.
    2) UTF-7's encoding is BASE64 which uses the "/" character; this
       conflicts with the use of "/" as a popular hierarchy delimiter.
    3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with
       the use of "\" as a popular hierarchy delimiter.
    4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with
       the use of "~" in some servers as a home directory indicator.
    5) UTF-7 permits multiple alternate forms to represent the same
       string; in particular, printable US-ASCII chararacters can be
       represented in encoded form.
 In modified UTF-7, printable US-ASCII characters except for "&"
 represent themselves; that is, characters with octet values 0x20-0x25
 and 0x27-0x7e.  The character "&" (0x26) is represented by the two-
 octet sequence "&-".
 All other characters (octet values 0x00-0x1f, 0x7f-0xff, and all
 Unicode 16-bit octets) are represented in modified BASE64, with a
 further modification from [UTF-7] that "," is used instead of "/".
 Modified BASE64 MUST NOT be used to represent any printing US-ASCII
 character which can represent itself.
 "&" is used to shift to modified BASE64 and "-" to shift back to US-
 ASCII.  All names start in US-ASCII, and MUST end in US-ASCII (that
 is, a name that ends with a Unicode 16-bit octet MUST end with a "-
 ").

Crispin Standards Track [Page 15] RFC 2060 IMAP4rev1 December 1996

    For example, here is a mailbox name which mixes English, Japanese,
    and Chinese text: ~peter/mail/&ZeVnLIqe-/&U,BTFw-

5.2. Mailbox Size and Message Status Updates

 At any time, a server can send data that the client did not request.
 Sometimes, such behavior is REQUIRED.  For example, agents other than
 the server MAY add messages to the mailbox (e.g. new mail delivery),
 change the flags of message in the mailbox (e.g. simultaneous access
 to the same mailbox by multiple agents), or even remove messages from
 the mailbox.  A server MUST send mailbox size updates automatically
 if a mailbox size change is observed during the processing of a
 command.  A server SHOULD send message flag updates automatically,
 without requiring the client to request such updates explicitly.
 Special rules exist for server notification of a client about the
 removal of messages to prevent synchronization errors; see the
 description of the EXPUNGE response for more detail.
 Regardless of what implementation decisions a client makes on
 remembering data from the server, a client implementation MUST record
 mailbox size updates.  It MUST NOT assume that any command after
 initial mailbox selection will return the size of the mailbox.

5.3. Response when no Command in Progress

 Server implementations are permitted to send an untagged response
 (except for EXPUNGE) while there is no command in progress.  Server
 implementations that send such responses MUST deal with flow control
 considerations.  Specifically, they MUST either (1) verify that the
 size of the data does not exceed the underlying transport's available
 window size, or (2) use non-blocking writes.

5.4. Autologout Timer

 If a server has an inactivity autologout timer, that timer MUST be of
 at least 30 minutes' duration.  The receipt of ANY command from the
 client during that interval SHOULD suffice to reset the autologout
 timer.

Crispin Standards Track [Page 16] RFC 2060 IMAP4rev1 December 1996

5.5. Multiple Commands in Progress

 The client MAY send another command without waiting for the
 completion result response of a command, subject to ambiguity rules
 (see below) and flow control constraints on the underlying data
 stream.  Similarly, a server MAY begin processing another command
 before processing the current command to completion, subject to
 ambiguity rules.  However, any command continuation request responses
 and command continuations MUST be negotiated before any subsequent
 command is initiated.
 The exception is if an ambiguity would result because of a command
 that would affect the results of other commands.  Clients MUST NOT
 send multiple commands without waiting if an ambiguity would result.
 If the server detects a possible ambiguity, it MUST execute commands
 to completion in the order given by the client.
 The most obvious example of ambiguity is when a command would affect
 the results of another command; for example, a FETCH of a message's
 flags and a STORE of that same message's flags.
 A non-obvious ambiguity occurs with commands that permit an untagged
 EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
 since an untagged EXPUNGE response can invalidate sequence numbers in
 a subsequent command.  This is not a problem for FETCH, STORE, or
 SEARCH commands because servers are prohibited from sending EXPUNGE
 responses while any of those commands are in progress.  Therefore, if
 the client sends any command other than FETCH, STORE, or SEARCH, it
 MUST wait for a response before sending a command with message
 sequence numbers.
 For example, the following non-waiting command sequences are invalid:
    FETCH + NOOP + STORE
    STORE + COPY + FETCH
    COPY + COPY
    CHECK + FETCH
 The following are examples of valid non-waiting command sequences:
    FETCH + STORE + SEARCH + CHECK
    STORE + COPY + EXPUNGE

6. Client Commands

 IMAP4rev1 commands are described in this section.  Commands are
 organized by the state in which the command is permitted.  Commands
 which are permitted in multiple states are listed in the minimum

Crispin Standards Track [Page 17] RFC 2060 IMAP4rev1 December 1996

 permitted state (for example, commands valid in authenticated and
 selected state are listed in the authenticated state commands).
 Command arguments, identified by "Arguments:" in the command
 descriptions below, are described by function, not by syntax.  The
 precise syntax of command arguments is described in the Formal Syntax
 section.
 Some commands cause specific server responses to be returned; these
 are identified by "Responses:" in the command descriptions below.
 See the response descriptions in the Responses section for
 information on these responses, and the Formal Syntax section for the
 precise syntax of these responses.  It is possible for server data to
 be transmitted as a result of any command; thus, commands that do not
 specifically require server data specify "no specific responses for
 this command" instead of "none".
 The "Result:" in the command description refers to the possible
 tagged status responses to a command, and any special interpretation
 of these status responses.

6.1. Client Commands - Any State

 The following commands are valid in any state: CAPABILITY, NOOP, and
 LOGOUT.

6.1.1. CAPABILITY Command

 Arguments:  none
 Responses:  REQUIRED untagged response: CAPABILITY
 Result:     OK - capability completed
             BAD - command unknown or arguments invalid
    The CAPABILITY command requests a listing of capabilities that the
    server supports.  The server MUST send a single untagged
    CAPABILITY response with "IMAP4rev1" as one of the listed
    capabilities before the (tagged) OK response.  This listing of
    capabilities is not dependent upon connection state or user.  It
    is therefore not necessary to issue a CAPABILITY command more than
    once in a connection.

Crispin Standards Track [Page 18] RFC 2060 IMAP4rev1 December 1996

    A capability name which begins with "AUTH=" indicates that the
    server supports that particular authentication mechanism.  All
    such names are, by definition, part of this specification.  For
    example, the authorization capability for an experimental
    "blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not
    "XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".
    Other capability names refer to extensions, revisions, or
    amendments to this specification.  See the documentation of the
    CAPABILITY response for additional information.  No capabilities,
    beyond the base IMAP4rev1 set defined in this specification, are
    enabled without explicit client action to invoke the capability.
    See the section entitled "Client Commands -
    Experimental/Expansion" for information about the form of site or
    implementation-specific capabilities.
 Example:    C: abcd CAPABILITY
             S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4
             S: abcd OK CAPABILITY completed

6.1.2. NOOP Command

 Arguments:  none
 Responses:  no specific responses for this command (but see below)
 Result:     OK - noop completed
             BAD - command unknown or arguments invalid
    The NOOP command always succeeds.  It does nothing.
    Since any command can return a status update as untagged data, the
    NOOP command can be used as a periodic poll for new messages or
    message status updates during a period of inactivity.  The NOOP
    command can also be used to reset any inactivity autologout timer
    on the server.
 Example:    C: a002 NOOP
             S: a002 OK NOOP completed
                . . .
             C: a047 NOOP
             S: * 22 EXPUNGE
             S: * 23 EXISTS
             S: * 3 RECENT
             S: * 14 FETCH (FLAGS (\Seen \Deleted))
             S: a047 OK NOOP completed

Crispin Standards Track [Page 19] RFC 2060 IMAP4rev1 December 1996

6.1.3. LOGOUT Command

 Arguments:  none
 Responses:  REQUIRED untagged response: BYE
 Result:     OK - logout completed
             BAD - command unknown or arguments invalid
    The LOGOUT command informs the server that the client is done with
    the connection.  The server MUST send a BYE untagged response
    before the (tagged) OK response, and then close the network
    connection.
 Example:    C: A023 LOGOUT
             S: * BYE IMAP4rev1 Server logging out
             S: A023 OK LOGOUT completed
             (Server and client then close the connection)

6.2. Client Commands - Non-Authenticated State

 In non-authenticated state, the AUTHENTICATE or LOGIN command
 establishes authentication and enter authenticated state.  The
 AUTHENTICATE command provides a general mechanism for a variety of
 authentication techniques, whereas the LOGIN command uses the
 traditional user name and plaintext password pair.
 Server implementations MAY allow non-authenticated access to certain
 mailboxes.  The convention is to use a LOGIN command with the userid
 "anonymous".  A password is REQUIRED.  It is implementation-dependent
 what requirements, if any, are placed on the password and what access
 restrictions are placed on anonymous users.
 Once authenticated (including as anonymous), it is not possible to
 re-enter non-authenticated state.
 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 the following commands are valid in non-authenticated state:
 AUTHENTICATE and LOGIN.

Crispin Standards Track [Page 20] RFC 2060 IMAP4rev1 December 1996

6.2.1. AUTHENTICATE Command

 Arguments:  authentication mechanism name
 Responses:  continuation data can be requested
 Result:     OK - authenticate completed, now in authenticated state
             NO - authenticate failure: unsupported authentication
                  mechanism, credentials rejected
            BAD - command unknown or arguments invalid,
                  authentication exchange cancelled
    The AUTHENTICATE command indicates an authentication mechanism,
    such as described in [IMAP-AUTH], to the server.  If the server
    supports the requested authentication mechanism, it performs an
    authentication protocol exchange to authenticate and identify the
    client.  It MAY also negotiate an OPTIONAL protection mechanism
    for subsequent protocol interactions.  If the requested
    authentication mechanism is not supported, the server SHOULD
    reject the AUTHENTICATE command by sending a tagged NO response.
    The authentication protocol exchange consists of a series of
    server challenges and client answers that are specific to the
    authentication mechanism.  A server challenge consists of a
    command continuation request response with the "+" token followed
    by a BASE64 encoded string.  The client answer consists of a line
    consisting of a BASE64 encoded string.  If the client wishes to
    cancel an authentication exchange, it issues a line with a single
    "*".  If the server receives such an answer, it MUST reject the
    AUTHENTICATE command by sending a tagged BAD response.
    A protection mechanism provides integrity and privacy protection
    to the connection.  If a protection mechanism is negotiated, it is
    applied to all subsequent data sent over the connection.  The
    protection mechanism takes effect immediately following the CRLF
    that concludes the authentication exchange for the client, and the
    CRLF of the tagged OK response for the server.  Once the
    protection mechanism is in effect, the stream of command and
    response octets is processed into buffers of ciphertext.  Each
    buffer is transferred over the connection as a stream of octets
    prepended with a four octet field in network byte order that
    represents the length of the following data.  The maximum
    ciphertext buffer length is defined by the protection mechanism.
    Authentication mechanisms are OPTIONAL.  Protection mechanisms are
    also OPTIONAL; an authentication mechanism MAY be implemented
    without any protection mechanism.  If an AUTHENTICATE command
    fails with a NO response, the client MAY try another

Crispin Standards Track [Page 21] RFC 2060 IMAP4rev1 December 1996

    authentication mechanism by issuing another AUTHENTICATE command,
    or MAY attempt to authenticate by using the LOGIN command.  In
    other words, the client MAY request authentication types in
    decreasing order of preference, with the LOGIN command as a last
    resort.
 Example:    S: * OK KerberosV4 IMAP4rev1 Server
             C: A001 AUTHENTICATE KERBEROS_V4
             S: + AmFYig==
             C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
                +nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
                WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
             S: + or//EoAADZI=
             C: DiAF5A4gA+oOIALuBkAAmw==
             S: A001 OK Kerberos V4 authentication successful
    Note: the line breaks in the first client answer are for editorial
    clarity and are not in real authenticators.

6.2.2. LOGIN Command

 Arguments:  user name
             password
 Responses:  no specific responses for this command
 Result:     OK - login completed, now in authenticated state
             NO - login failure: user name or password rejected
             BAD - command unknown or arguments invalid
    The LOGIN command identifies the client to the server and carries
    the plaintext password authenticating this user.
 Example:    C: a001 LOGIN SMITH SESAME
             S: a001 OK LOGIN completed

6.3. Client Commands - Authenticated State

 In authenticated state, commands that manipulate mailboxes as atomic
 entities are permitted.  Of these commands, the SELECT and EXAMINE
 commands will select a mailbox for access and enter selected state.
 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 the following commands are valid in authenticated state: SELECT,
 EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
 STATUS, and APPEND.

Crispin Standards Track [Page 22] RFC 2060 IMAP4rev1 December 1996

6.3.1. SELECT Command

 Arguments:  mailbox name
 Responses:  REQUIRED untagged responses: FLAGS, EXISTS, RECENT
             OPTIONAL OK untagged responses: UNSEEN, PERMANENTFLAGS
 Result:     OK - select completed, now in selected state
             NO - select failure, now in authenticated state: no
                  such mailbox, can't access mailbox
             BAD - command unknown or arguments invalid
 The SELECT command selects a mailbox so that messages in the
 mailbox can be accessed.  Before returning an OK to the client,
 the server MUST send the following untagged data to the client:
    FLAGS       Defined flags in the mailbox.  See the description
                of the FLAGS response for more detail.
    <n> EXISTS  The number of messages in the mailbox.  See the
                description of the EXISTS response for more detail.
    <n> RECENT  The number of messages with the \Recent flag set.
                See the description of the RECENT response for more
                detail.
    OK [UIDVALIDITY <n>]
                The unique identifier validity value.  See the
                description of the UID command for more detail.
 to define the initial state of the mailbox at the client.
 The server SHOULD also send an UNSEEN response code in an OK
 untagged response, indicating the message sequence number of the
 first unseen message in the mailbox.
 If the client can not change the permanent state of one or more of
 the flags listed in the FLAGS untagged response, the server SHOULD
 send a PERMANENTFLAGS response code in an OK untagged response,
 listing the flags that the client can change permanently.
 Only one mailbox can be selected at a time in a connection;
 simultaneous access to multiple mailboxes requires multiple
 connections.  The SELECT command automatically deselects any
 currently selected mailbox before attempting the new selection.
 Consequently, if a mailbox is selected and a SELECT command that
 fails is attempted, no mailbox is selected.

Crispin Standards Track [Page 23] RFC 2060 IMAP4rev1 December 1996

 If the client is permitted to modify the mailbox, the server
 SHOULD prefix the text of the tagged OK response with the
       "[READ-WRITE]" response code.
    If the client is not permitted to modify the mailbox but is
    permitted read access, the mailbox is selected as read-only, and
    the server MUST prefix the text of the tagged OK response to
    SELECT with the "[READ-ONLY]" response code.  Read-only access
    through SELECT differs from the EXAMINE command in that certain
    read-only mailboxes MAY permit the change of permanent state on a
    per-user (as opposed to global) basis.  Netnews messages marked in
    a server-based .newsrc file are an example of such per-user
    permanent state that can be modified with read-only mailboxes.
 Example:    C: A142 SELECT INBOX
             S: * 172 EXISTS
             S: * 1 RECENT
             S: * OK [UNSEEN 12] Message 12 is first unseen
             S: * OK [UIDVALIDITY 3857529045] UIDs valid
             S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
             S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
             S: A142 OK [READ-WRITE] SELECT completed

6.3.2. EXAMINE Command

 Arguments:  mailbox name
 Responses:  REQUIRED untagged responses: FLAGS, EXISTS, RECENT
             OPTIONAL OK untagged responses: UNSEEN, PERMANENTFLAGS
 Result:     OK - examine completed, now in selected state
             NO - examine failure, now in authenticated state: no
                  such mailbox, can't access mailbox
             BAD - command unknown or arguments invalid
    The EXAMINE command is identical to SELECT and returns the same
    output; however, the selected mailbox is identified as read-only.
    No changes to the permanent state of the mailbox, including
    per-user state, are permitted.

Crispin Standards Track [Page 24] RFC 2060 IMAP4rev1 December 1996

    The text of the tagged OK response to the EXAMINE command MUST
    begin with the "[READ-ONLY]" response code.
 Example:    C: A932 EXAMINE blurdybloop
             S: * 17 EXISTS
             S: * 2 RECENT
             S: * OK [UNSEEN 8] Message 8 is first unseen
             S: * OK [UIDVALIDITY 3857529045] UIDs valid
             S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
             S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
             S: A932 OK [READ-ONLY] EXAMINE completed

6.3.3. CREATE Command

 Arguments:  mailbox name
 Responses:  no specific responses for this command
 Result:     OK - create completed
             NO - create failure: can't create mailbox with that name
             BAD - command unknown or arguments invalid
    The CREATE command creates a mailbox with the given name.  An OK
    response is returned only if a new mailbox with that name has been
    created.  It is an error to attempt to create INBOX or a mailbox
    with a name that refers to an extant mailbox.  Any error in
    creation will return a tagged NO response.
    If the mailbox name is suffixed with the server's hierarchy
    separator character (as returned from the server by a LIST
    command), this is a declaration that the client intends to create
    mailbox names under this name in the hierarchy.  Server
    implementations that do not require this declaration MUST ignore
    it.
    If the server's hierarchy separator character appears elsewhere in
    the name, the server SHOULD create any superior hierarchical names
    that are needed for the CREATE command to complete successfully.
    In other words, an attempt to create "foo/bar/zap" on a server in
    which "/" is the hierarchy separator character SHOULD create foo/
    and foo/bar/ if they do not already exist.
    If a new mailbox is created with the same name as a mailbox which
    was deleted, its unique identifiers MUST be greater than any
    unique identifiers used in the previous incarnation of the mailbox
    UNLESS the new incarnation has a different unique identifier
    validity value.  See the description of the UID command for more
    detail.

Crispin Standards Track [Page 25] RFC 2060 IMAP4rev1 December 1996

 Example:    C: A003 CREATE owatagusiam/
             S: A003 OK CREATE completed
             C: A004 CREATE owatagusiam/blurdybloop
             S: A004 OK CREATE completed
    Note: the interpretation of this example depends on whether "/"
    was returned as the hierarchy separator from LIST.  If "/" is the
    hierarchy separator, a new level of hierarchy named "owatagusiam"
    with a member called "blurdybloop" is created.  Otherwise, two
    mailboxes at the same hierarchy level are created.

6.3.4. DELETE Command

 Arguments:  mailbox name
 Responses:  no specific responses for this command
 Result:     OK - delete completed
             NO - delete failure: can't delete mailbox with that name
             BAD - command unknown or arguments invalid
    The DELETE command permanently removes the mailbox with the given
    name.  A tagged OK response is returned only if the mailbox has
    been deleted.  It is an error to attempt to delete INBOX or a
    mailbox name that does not exist.
    The DELETE command MUST NOT remove inferior hierarchical names.
    For example, if a mailbox "foo" has an inferior "foo.bar"
    (assuming "." is the hierarchy delimiter character), removing
    "foo" MUST NOT remove "foo.bar".  It is an error to attempt to
    delete a name that has inferior hierarchical names and also has
    the \Noselect mailbox name attribute (see the description of the
    LIST response for more details).
    It is permitted to delete a name that has inferior hierarchical
    names and does not have the \Noselect mailbox name attribute.  In
    this case, all messages in that mailbox are removed, and the name
    will acquire the \Noselect mailbox name attribute.
    The value of the highest-used unique identifier of the deleted
    mailbox MUST be preserved so that a new mailbox created with the
    same name will not reuse the identifiers of the former
    incarnation, UNLESS the new incarnation has a different unique
    identifier validity value.  See the description of the UID command
    for more detail.

Crispin Standards Track [Page 26] RFC 2060 IMAP4rev1 December 1996

 Examples:   C: A682 LIST "" *
             S: * LIST () "/" blurdybloop
             S: * LIST (\Noselect) "/" foo
             S: * LIST () "/" foo/bar
             S: A682 OK LIST completed
             C: A683 DELETE blurdybloop
             S: A683 OK DELETE completed
             C: A684 DELETE foo
             S: A684 NO Name "foo" has inferior hierarchical names
             C: A685 DELETE foo/bar
             S: A685 OK DELETE Completed
             C: A686 LIST "" *
             S: * LIST (\Noselect) "/" foo
             S: A686 OK LIST completed
             C: A687 DELETE foo
             S: A687 OK DELETE Completed
             C: A82 LIST "" *
             S: * LIST () "." blurdybloop
             S: * LIST () "." foo
             S: * LIST () "." foo.bar
             S: A82 OK LIST completed
             C: A83 DELETE blurdybloop
             S: A83 OK DELETE completed
             C: A84 DELETE foo
             S: A84 OK DELETE Completed
             C: A85 LIST "" *
             S: * LIST () "." foo.bar
             S: A85 OK LIST completed
             C: A86 LIST "" %
             S: * LIST (\Noselect) "." foo
             S: A86 OK LIST completed

6.3.5. RENAME Command

 Arguments:  existing mailbox name
             new mailbox name
 Responses:  no specific responses for this command
 Result:     OK - rename completed
             NO - rename failure: can't rename mailbox with that name,
                  can't rename to mailbox with that name
             BAD - command unknown or arguments invalid
    The RENAME command changes the name of a mailbox.  A tagged OK
    response is returned only if the mailbox has been renamed.  It is

Crispin Standards Track [Page 27] RFC 2060 IMAP4rev1 December 1996

    an error to attempt to rename from a mailbox name that does not
    exist or to a mailbox name that already exists.  Any error in
    renaming will return a tagged NO response.
    If the name has inferior hierarchical names, then the inferior
    hierarchical names MUST also be renamed.  For example, a rename of
    "foo" to "zap" will rename "foo/bar" (assuming "/" is the
    hierarchy delimiter character) to "zap/bar".
    The value of the highest-used unique identifier of the old mailbox
    name MUST be preserved so that a new mailbox created with the same
    name will not reuse the identifiers of the former incarnation,
    UNLESS the new incarnation has a different unique identifier
    validity value.  See the description of the UID command for more
    detail.
    Renaming INBOX is permitted, and has special behavior.  It moves
    all messages in INBOX to a new mailbox with the given name,
    leaving INBOX empty.  If the server implementation supports
    inferior hierarchical names of INBOX, these are unaffected by a
    rename of INBOX.
 Examples:   C: A682 LIST "" *
             S: * LIST () "/" blurdybloop
             S: * LIST (\Noselect) "/" foo
             S: * LIST () "/" foo/bar
             S: A682 OK LIST completed
             C: A683 RENAME blurdybloop sarasoop
             S: A683 OK RENAME completed
             C: A684 RENAME foo zowie
             S: A684 OK RENAME Completed
             C: A685 LIST "" *
             S: * LIST () "/" sarasoop
             S: * LIST (\Noselect) "/" zowie
             S: * LIST () "/" zowie/bar
             S: A685 OK LIST completed

Crispin Standards Track [Page 28] RFC 2060 IMAP4rev1 December 1996

             C: Z432 LIST "" *
             S: * LIST () "." INBOX
             S: * LIST () "." INBOX.bar
             S: Z432 OK LIST completed
             C: Z433 RENAME INBOX old-mail
             S: Z433 OK RENAME completed
             C: Z434 LIST "" *
             S: * LIST () "." INBOX
             S: * LIST () "." INBOX.bar
             S: * LIST () "." old-mail
             S: Z434 OK LIST completed

6.3.6. SUBSCRIBE Command

 Arguments:  mailbox
 Responses:  no specific responses for this command
 Result:     OK - subscribe completed
             NO - subscribe failure: can't subscribe to that name
             BAD - command unknown or arguments invalid
    The SUBSCRIBE command adds the specified mailbox name to the
    server's set of "active" or "subscribed" mailboxes as returned by
    the LSUB command.  This command returns a tagged OK response only
    if the subscription is successful.
    A server MAY validate the mailbox argument to SUBSCRIBE to verify
    that it exists.  However, it MUST NOT unilaterally remove an
    existing mailbox name from the subscription list even if a mailbox
    by that name no longer exists.
    Note: this requirement is because some server sites may routinely
    remove a mailbox with a well-known name (e.g.  "system-alerts")
    after its contents expire, with the intention of recreating it
    when new contents are appropriate.
 Example:    C: A002 SUBSCRIBE #news.comp.mail.mime
             S: A002 OK SUBSCRIBE completed

Crispin Standards Track [Page 29] RFC 2060 IMAP4rev1 December 1996

6.3.7. UNSUBSCRIBE Command

 Arguments:  mailbox name
 Responses:  no specific responses for this command
 Result:     OK - unsubscribe completed
             NO - unsubscribe failure: can't unsubscribe that name
             BAD - command unknown or arguments invalid
    The UNSUBSCRIBE command removes the specified mailbox name from
    the server's set of "active" or "subscribed" mailboxes as returned
    by the LSUB command.  This command returns a tagged OK response
    only if the unsubscription is successful.
 Example:    C: A002 UNSUBSCRIBE #news.comp.mail.mime
             S: A002 OK UNSUBSCRIBE completed

6.3..8. LIST Command

 Arguments:  reference name
             mailbox name with possible wildcards
 Responses:  untagged responses: LIST
 Result:     OK - list completed
             NO - list failure: can't list that reference or name
             BAD - command unknown or arguments invalid
    The LIST command returns a subset of names from the complete set
    of all names available to the client.  Zero or more untagged LIST
    replies are returned, containing the name attributes, hierarchy
    delimiter, and name; see the description of the LIST reply for
    more detail.
    The LIST command SHOULD return its data quickly, without undue
    delay.  For example, it SHOULD NOT go to excess trouble to
    calculate \Marked or \Unmarked status or perform other processing;
    if each name requires 1 second of processing, then a list of 1200
    names would take 20 minutes!
    An empty ("" string) reference name argument indicates that the
    mailbox name is interpreted as by SELECT. The returned mailbox
    names MUST match the supplied mailbox name pattern.  A non-empty
    reference name argument is the name of a mailbox or a level of
    mailbox hierarchy, and indicates a context in which the mailbox
    name is interpreted in an implementation-defined manner.

Crispin Standards Track [Page 30] RFC 2060 IMAP4rev1 December 1996

    An empty ("" string) mailbox name argument is a special request to
    return the hierarchy delimiter and the root name of the name given
    in the reference.  The value returned as the root MAY be null if
    the reference is non-rooted or is null.  In all cases, the
    hierarchy delimiter is returned.  This permits a client to get the
    hierarchy delimiter even when no mailboxes by that name currently
    exist.
    The reference and mailbox name arguments are interpreted, in an
    implementation-dependent fashion, into a canonical form that
    represents an unambiguous left-to-right hierarchy.  The returned
    mailbox names will be in the interpreted form.
    Any part of the reference argument that is included in the
    interpreted form SHOULD prefix the interpreted form.  It SHOULD
    also be in the same form as the reference name argument.  This
    rule permits the client to determine if the returned mailbox name
    is in the context of the reference argument, or if something about
    the mailbox argument overrode the reference argument.  Without
    this rule, the client would have to have knowledge of the server's
    naming semantics including what characters are "breakouts" that
    override a naming context.
    For example, here are some examples of how references and mailbox
    names might be interpreted on a UNIX-based server:
             Reference     Mailbox Name  Interpretation
             ------------  ------------  --------------
             ~smith/Mail/  foo.*         ~smith/Mail/foo.*
             archive/      %             archive/%
             #news.        comp.mail.*   #news.comp.mail.*
             ~smith/Mail/  /usr/doc/foo  /usr/doc/foo
             archive/      ~fred/Mail/*  ~fred/Mail/*
    The first three examples demonstrate interpretations in the
    context of the reference argument.  Note that "~smith/Mail" SHOULD
    NOT be transformed into something like "/u2/users/smith/Mail", or
    it would be impossible for the client to determine that the
    interpretation was in the context of the reference.
    The character "*" is a wildcard, and matches zero or more
    characters at this position.  The character "%" is similar to "*",
    but it does not match a hierarchy delimiter.  If the "%" wildcard
    is the last character of a mailbox name argument, matching levels
    of hierarchy are also returned.  If these levels of hierarchy are
    not also selectable mailboxes, they are returned with the
    \Noselect mailbox name attribute (see the description of the LIST
    response for more details).

Crispin Standards Track [Page 31] RFC 2060 IMAP4rev1 December 1996

    Server implementations are permitted to "hide" otherwise
    accessible mailboxes from the wildcard characters, by preventing
    certain characters or names from matching a wildcard in certain
    situations.  For example, a UNIX-based server might restrict the
    interpretation of "*" so that an initial "/" character does not
    match.
    The special name INBOX is included in the output from LIST, if
    INBOX is supported by this server for this user and if the
    uppercase string "INBOX" matches the interpreted reference and
    mailbox name arguments with wildcards as described above.  The
    criteria for omitting INBOX is whether SELECT INBOX will return
    failure; it is not relevant whether the user's real INBOX resides
    on this or some other server.
 Example:    C: A101 LIST "" ""
             S: * LIST (\Noselect) "/" ""
             S: A101 OK LIST Completed
             C: A102 LIST #news.comp.mail.misc ""
             S: * LIST (\Noselect) "." #news.
             S: A102 OK LIST Completed
             C: A103 LIST /usr/staff/jones ""
             S: * LIST (\Noselect) "/" /
             S: A103 OK LIST Completed
             C: A202 LIST ~/Mail/ %
             S: * LIST (\Noselect) "/" ~/Mail/foo
             S: * LIST () "/" ~/Mail/meetings
             S: A202 OK LIST completed

6.3.9. LSUB Command

 Arguments:  reference name
             mailbox name with possible wildcards
 Responses:  untagged responses: LSUB
 Result:     OK - lsub completed
             NO - lsub failure: can't list that reference or name
             BAD - command unknown or arguments invalid
    The LSUB command returns a subset of names from the set of names
    that the user has declared as being "active" or "subscribed".
    Zero or more untagged LSUB replies are returned.  The arguments to
    LSUB are in the same form as those for LIST.
    A server MAY validate the subscribed names to see if they still
    exist.  If a name does not exist, it SHOULD be flagged with the
    \Noselect attribute in the LSUB response.  The server MUST NOT

Crispin Standards Track [Page 32] RFC 2060 IMAP4rev1 December 1996

    unilaterally remove an existing mailbox name from the subscription
    list even if a mailbox by that name no longer exists.
 Example:    C: A002 LSUB "#news." "comp.mail.*"
             S: * LSUB () "." #news.comp.mail.mime
             S: * LSUB () "." #news.comp.mail.misc
             S: A002 OK LSUB completed

6.3.10. STATUS Command

 Arguments:  mailbox name
             status data item names
 Responses:  untagged responses: STATUS
 Result:     OK - status completed
             NO - status failure: no status for that name
             BAD - command unknown or arguments invalid
    The STATUS command requests the status of the indicated mailbox.
    It does not change the currently selected mailbox, nor does it
    affect the state of any messages in the queried mailbox (in
    particular, STATUS MUST NOT cause messages to lose the \Recent
    flag).
    The STATUS command provides an alternative to opening a second
    IMAP4rev1 connection and doing an EXAMINE command on a mailbox to
    query that mailbox's status without deselecting the current
    mailbox in the first IMAP4rev1 connection.
    Unlike the LIST command, the STATUS command is not guaranteed to
    be fast in its response.  In some implementations, the server is
    obliged to open the mailbox read-only internally to obtain certain
    status information.  Also unlike the LIST command, the STATUS
    command does not accept wildcards.
    The currently defined status data items that can be requested are:
    MESSAGES       The number of messages in the mailbox.
    RECENT         The number of messages with the \Recent flag set.
    UIDNEXT        The next UID value that will be assigned to a new
                   message in the mailbox.  It is guaranteed that this
                   value will not change unless new messages are added
                   to the mailbox; and that it will change when new
                   messages are added even if those new messages are
                   subsequently expunged.

Crispin Standards Track [Page 33] RFC 2060 IMAP4rev1 December 1996

    UIDVALIDITY    The unique identifier validity value of the
                   mailbox.
    UNSEEN         The number of messages which do not have the \Seen
                   flag set.
    Example:    C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
                S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
                S: A042 OK STATUS completed

6.3.11. APPEND Command

 Arguments:  mailbox name
             OPTIONAL flag parenthesized list
             OPTIONAL date/time string
             message literal
 Responses:  no specific responses for this command
 Result:     OK - append completed
             NO - append error: can't append to that mailbox, error
                  in flags or date/time or message text
             BAD - command unknown or arguments invalid
    The APPEND command appends the literal argument as a new message
    to the end of the specified destination mailbox.  This argument
    SHOULD be in the format of an [RFC-822] message.  8-bit characters
    are permitted in the message.  A server implementation that is
    unable to preserve 8-bit data properly MUST be able to reversibly
    convert 8-bit APPEND data to 7-bit using a [MIME-IMB] content
    transfer encoding.
    Note: There MAY be exceptions, e.g. draft messages, in which
    required [RFC-822] header lines are omitted in the message literal
    argument to APPEND.  The full implications of doing so MUST be
    understood and carefully weighed.
 If a flag parenthesized list is specified, the flags SHOULD be set in
 the resulting message; otherwise, the flag list of the resulting
 message is set empty by default.
 If a date_time is specified, the internal date SHOULD be set in the
 resulting message; otherwise, the internal date of the resulting
 message is set to the current date and time by default.

Crispin Standards Track [Page 34] RFC 2060 IMAP4rev1 December 1996

 If the append is unsuccessful for any reason, the mailbox MUST be
 restored to its state before the APPEND attempt; no partial appending
 is permitted.
 If the destination mailbox does not exist, a server MUST return an
 error, and MUST NOT automatically create the mailbox.  Unless it is
 certain that the destination mailbox can not be created, the server
 MUST send the response code "[TRYCREATE]" as the prefix of the text
 of the tagged NO response.  This gives a hint to the client that it
 can attempt a CREATE command and retry the APPEND if the CREATE is
 successful.
 If the mailbox is currently selected, the normal new mail actions
 SHOULD occur.  Specifically, the server SHOULD notify the client
 immediately via an untagged EXISTS response.  If the server does not
 do so, the client MAY issue a NOOP command (or failing that, a CHECK
 command) after one or more APPEND commands.
 Example:    C: A003 APPEND saved-messages (\Seen) {310}
             C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
             C: From: Fred Foobar <foobar@Blurdybloop.COM>
             C: Subject: afternoon meeting
             C: To: mooch@owatagu.siam.edu
             C: Message-Id: <B27397-0100000@Blurdybloop.COM>
             C: MIME-Version: 1.0
             C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
             C:
             C: Hello Joe, do you think we can meet at 3:30 tomorrow?
             C:
             S: A003 OK APPEND completed
    Note: the APPEND command is not used for message delivery, because
    it does not provide a mechanism to transfer [SMTP] envelope
    information.

6.4. Client Commands - Selected State

 In selected state, commands that manipulate messages in a mailbox are
 permitted.
 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 and the authenticated state commands (SELECT, EXAMINE, CREATE,
 DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and
 APPEND), the following commands are valid in the selected state:
 CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID.

Crispin Standards Track [Page 35] RFC 2060 IMAP4rev1 December 1996

6.4.1. CHECK Command

 Arguments:  none
 Responses:  no specific responses for this command
 Result:     OK - check completed
             BAD - command unknown or arguments invalid
    The CHECK command requests a checkpoint of the currently selected
    mailbox.  A checkpoint refers to any implementation-dependent
    housekeeping associated with the mailbox (e.g. resolving the
    server's in-memory state of the mailbox with the state on its
    disk) that is not normally executed as part of each command.  A
    checkpoint MAY take a non-instantaneous amount of real time to
    complete.  If a server implementation has no such housekeeping
    considerations, CHECK is equivalent to NOOP.
    There is no guarantee that an EXISTS untagged response will happen
    as a result of CHECK.  NOOP, not CHECK, SHOULD be used for new
    mail polling.
 Example:    C: FXXZ CHECK
             S: FXXZ OK CHECK Completed

6.4.2. CLOSE Command

 Arguments:  none
 Responses:  no specific responses for this command
 Result:     OK - close completed, now in authenticated state
             NO - close failure: no mailbox selected
             BAD - command unknown or arguments invalid
    The CLOSE command permanently removes from the currently selected
    mailbox all messages that have the \Deleted flag set, and returns
    to authenticated state from selected state.  No untagged EXPUNGE
    responses are sent.
    No messages are removed, and no error is given, if the mailbox is
    selected by an EXAMINE command or is otherwise selected read-only.
    Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT
    command MAY be issued without previously issuing a CLOSE command.
    The SELECT, EXAMINE, and LOGOUT commands implicitly close the
    currently selected mailbox without doing an expunge.  However,
    when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT

Crispin Standards Track [Page 36] RFC 2060 IMAP4rev1 December 1996

    sequence is considerably faster than an EXPUNGE-LOGOUT or
    EXPUNGE-SELECT because no untagged EXPUNGE responses (which the
    client would probably ignore) are sent.
 Example:    C: A341 CLOSE
             S: A341 OK CLOSE completed

6.4.3. EXPUNGE Command

 Arguments:  none
 Responses:  untagged responses: EXPUNGE
 Result:     OK - expunge completed
             NO - expunge failure: can't expunge (e.g. permission
                  denied)
             BAD - command unknown or arguments invalid
    The EXPUNGE command permanently removes from the currently
    selected mailbox all messages that have the \Deleted flag set.
    Before returning an OK to the client, an untagged EXPUNGE response
    is sent for each message that is removed.
 Example:    C: A202 EXPUNGE
             S: * 3 EXPUNGE
             S: * 3 EXPUNGE
             S: * 5 EXPUNGE
             S: * 8 EXPUNGE
             S: A202 OK EXPUNGE completed
    Note: in this example, messages 3, 4, 7, and 11 had the
    \Deleted flag set.  See the description of the EXPUNGE
    response for further explanation.

6.4.4. SEARCH Command

 Arguments:  OPTIONAL [CHARSET] specification
             searching criteria (one or more)
 Responses:  REQUIRED untagged response: SEARCH
 Result:     OK - search completed
             NO - search error: can't search that [CHARSET] or
                  criteria
             BAD - command unknown or arguments invalid

Crispin Standards Track [Page 37] RFC 2060 IMAP4rev1 December 1996

    The SEARCH command searches the mailbox for messages that match
    the given searching criteria.  Searching criteria consist of one
    or more search keys.  The untagged SEARCH response from the server
    contains a listing of message sequence numbers corresponding to
    those messages that match the searching criteria.
    When multiple keys are specified, the result is the intersection
    (AND function) of all the messages that match those keys.  For
    example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers
    to all deleted messages from Smith that were placed in the mailbox
    since February 1, 1994.  A search key can also be a parenthesized
    list of one or more search keys (e.g. for use with the OR and NOT
    keys).
    Server implementations MAY exclude [MIME-IMB] body parts with
    terminal content media types other than TEXT and MESSAGE from
    consideration in SEARCH matching.
    The OPTIONAL [CHARSET] specification consists of the word
    "CHARSET" followed by a registered [CHARSET].  It indicates the
    [CHARSET] of the strings that appear in the search criteria.
    [MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in
    [RFC-822]/[MIME-IMB] headers, MUST be decoded before comparing
    text in a [CHARSET] other than US-ASCII.  US-ASCII MUST be
    supported; other [CHARSET]s MAY be supported.  If the server does
    not support the specified [CHARSET], it MUST return a tagged NO
    response (not a BAD).
    In all search keys that use strings, a message matches the key if
    the string is a substring of the field.  The matching is case-
    insensitive.
    The defined search keys are as follows.  Refer to the Formal
    Syntax section for the precise syntactic definitions of the
    arguments.
    <message set>  Messages with message sequence numbers
                   corresponding to the specified message sequence
                   number set
    ALL            All messages in the mailbox; the default initial
                   key for ANDing.
    ANSWERED       Messages with the \Answered flag set.
    BCC <string>   Messages that contain the specified string in the
                   envelope structure's BCC field.

Crispin Standards Track [Page 38] RFC 2060 IMAP4rev1 December 1996

    BEFORE <date>  Messages whose internal date is earlier than the
                   specified date.
    BODY <string>  Messages that contain the specified string in the
                   body of the message.
    CC <string>    Messages that contain the specified string in the
                   envelope structure's CC field.
    DELETED        Messages with the \Deleted flag set.
    DRAFT          Messages with the \Draft flag set.
    FLAGGED        Messages with the \Flagged flag set.
    FROM <string>  Messages that contain the specified string in the
                   envelope structure's FROM field.
    HEADER <field-name> <string>
                   Messages that have a header with the specified
                   field-name (as defined in [RFC-822]) and that
                   contains the specified string in the [RFC-822]
                   field-body.
    KEYWORD <flag> Messages with the specified keyword set.
    LARGER <n>     Messages with an [RFC-822] size larger than the
                   specified number of octets.
    NEW            Messages that have the \Recent flag set but not the
                   \Seen flag.  This is functionally equivalent to
                   "(RECENT UNSEEN)".
    NOT <search-key>
                   Messages that do not match the specified search
                   key.
    OLD            Messages that do not have the \Recent flag set.
                   This is functionally equivalent to "NOT RECENT" (as
                   opposed to "NOT NEW").
    ON <date>      Messages whose internal date is within the
                   specified date.
    OR <search-key1> <search-key2>
                   Messages that match either search key.
    RECENT         Messages that have the \Recent flag set.

Crispin Standards Track [Page 39] RFC 2060 IMAP4rev1 December 1996

    SEEN           Messages that have the \Seen flag set.
    SENTBEFORE <date>
                   Messages whose [RFC-822] Date: header is earlier
                   than the specified date.
    SENTON <date>  Messages whose [RFC-822] Date: header is within the
                   specified date.
    SENTSINCE <date>
                   Messages whose [RFC-822] Date: header is within or
                   later than the specified date.
    SINCE <date>   Messages whose internal date is within or later
                   than the specified date.
    SMALLER <n>    Messages with an [RFC-822] size smaller than the
                   specified number of octets.
    SUBJECT <string>
                   Messages that contain the specified string in the
                   envelope structure's SUBJECT field.
    TEXT <string>  Messages that contain the specified string in the
                   header or body of the message.
    TO <string>    Messages that contain the specified string in the
                   envelope structure's TO field.
    UID <message set>
                   Messages with unique identifiers corresponding to
                   the specified unique identifier set.
    UNANSWERED     Messages that do not have the \Answered flag set.
    UNDELETED      Messages that do not have the \Deleted flag set.
    UNDRAFT        Messages that do not have the \Draft flag set.
    UNFLAGGED      Messages that do not have the \Flagged flag set.
    UNKEYWORD <flag>
                   Messages that do not have the specified keyword
                   set.
    UNSEEN         Messages that do not have the \Seen flag set.

Crispin Standards Track [Page 40] RFC 2060 IMAP4rev1 December 1996

 Example:    C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
             S: * SEARCH 2 84 882
             S: A282 OK SEARCH completed

6.4.5. FETCH Command

 Arguments:  message set
             message data item names
 Responses:  untagged responses: FETCH
 Result:     OK - fetch completed
             NO - fetch error: can't fetch that data
             BAD - command unknown or arguments invalid
    The FETCH command retrieves data associated with a message in the
    mailbox.  The data items to be fetched can be either a single atom
    or a parenthesized list.
    The currently defined data items that can be fetched are:
    ALL            Macro equivalent to: (FLAGS INTERNALDATE
                   RFC822.SIZE ENVELOPE)
    BODY           Non-extensible form of BODYSTRUCTURE.
    BODY[<section>]<<partial>>
                   The text of a particular body section.  The section
                   specification is a set of zero or more part
                   specifiers delimited by periods.  A part specifier
                   is either a part number or one of the following:
                   HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, MIME, and
                   TEXT.  An empty section specification refers to the
                   entire message, including the header.
                   Every message has at least one part number.
                   Non-[MIME-IMB] messages, and non-multipart
                   [MIME-IMB] messages with no encapsulated message,
                   only have a part 1.
                   Multipart messages are assigned consecutive part
                   numbers, as they occur in the message.  If a
                   particular part is of type message or multipart,
                   its parts MUST be indicated by a period followed by
                   the part number within that nested multipart part.

Crispin Standards Track [Page 41] RFC 2060 IMAP4rev1 December 1996

                   A part of type MESSAGE/RFC822 also has nested part
                   numbers, referring to parts of the MESSAGE part's
                   body.
                   The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and
                   TEXT part specifiers can be the sole part specifier
                   or can be prefixed by one or more numeric part
                   specifiers, provided that the numeric part
                   specifier refers to a part of type MESSAGE/RFC822.
                   The MIME part specifier MUST be prefixed by one or
                   more numeric part specifiers.
                   The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT
                   part specifiers refer to the [RFC-822] header of
                   the message or of an encapsulated [MIME-IMT]
                   MESSAGE/RFC822 message.  HEADER.FIELDS and
                   HEADER.FIELDS.NOT are followed by a list of
                   field-name (as defined in [RFC-822]) names, and
                   return a subset of the header.  The subset returned
                   by HEADER.FIELDS contains only those header fields
                   with a field-name that matches one of the names in
                   the list; similarly, the subset returned by
                   HEADER.FIELDS.NOT contains only the header fields
                   with a non-matching field-name.  The field-matching
                   is case-insensitive but otherwise exact.  In all
                   cases, the delimiting blank line between the header
                   and the body is always included.
                   The MIME part specifier refers to the [MIME-IMB]
                   header for this part.
                   The TEXT part specifier refers to the text body of
                   the message, omitting the [RFC-822] header.

Crispin Standards Track [Page 42] RFC 2060 IMAP4rev1 December 1996

                     Here is an example of a complex message
                     with some of its part specifiers:
                      HEADER     ([RFC-822] header of the message)
                      TEXT       MULTIPART/MIXED
                      1          TEXT/PLAIN
                      2          APPLICATION/OCTET-STREAM
                      3          MESSAGE/RFC822
                      3.HEADER   ([RFC-822] header of the message)
                      3.TEXT     ([RFC-822] text body of the message)
                      3.1        TEXT/PLAIN
                      3.2        APPLICATION/OCTET-STREAM
                      4          MULTIPART/MIXED
                      4.1        IMAGE/GIF
                      4.1.MIME   ([MIME-IMB] header for the IMAGE/GIF)
                      4.2        MESSAGE/RFC822
                      4.2.HEADER ([RFC-822] header of the message)
                      4.2.TEXT   ([RFC-822] text body of the message)
                      4.2.1      TEXT/PLAIN
                      4.2.2      MULTIPART/ALTERNATIVE
                      4.2.2.1    TEXT/PLAIN
                      4.2.2.2    TEXT/RICHTEXT
                   It is possible to fetch a substring of the
                   designated text.  This is done by appending an open
                   angle bracket ("<"), the octet position of the
                   first desired octet, a period, the maximum number
                   of octets desired, and a close angle bracket (">")
                   to the part specifier.  If the starting octet is
                   beyond the end of the text, an empty string is
                   returned.
                   Any partial fetch that attempts to read beyond the
                   end of the text is truncated as appropriate.  A
                   partial fetch that starts at octet 0 is returned as
                   a partial fetch, even if this truncation happened.
                        Note: this means that BODY[]<0.2048> of a
                        1500-octet message will return BODY[]<0>
                        with a literal of size 1500, not BODY[].
                        Note: a substring fetch of a
                        HEADER.FIELDS or HEADER.FIELDS.NOT part
                        specifier is calculated after subsetting
                        the header.

Crispin Standards Track [Page 43] RFC 2060 IMAP4rev1 December 1996

                   The \Seen flag is implicitly set; if this causes
                   the flags to change they SHOULD be included as part
                   of the FETCH responses.
    BODY.PEEK[<section>]<<partial>>
                   An alternate form of BODY[<section>] that does not
                   implicitly set the \Seen flag.
    BODYSTRUCTURE  The [MIME-IMB] body structure of the message.  This
                   is computed by the server by parsing the [MIME-IMB]
                   header fields in the [RFC-822] header and
                   [MIME-IMB] headers.
    ENVELOPE       The envelope structure of the message.  This is
                   computed by the server by parsing the [RFC-822]
                   header into the component parts, defaulting various
                   fields as necessary.
    FAST           Macro equivalent to: (FLAGS INTERNALDATE
                   RFC822.SIZE)
    FLAGS          The flags that are set for this message.
    FULL           Macro equivalent to: (FLAGS INTERNALDATE
                   RFC822.SIZE ENVELOPE BODY)
    INTERNALDATE   The internal date of the message.
    RFC822         Functionally equivalent to BODY[], differing in the
                   syntax of the resulting untagged FETCH data (RFC822
                   is returned).
    RFC822.HEADER  Functionally equivalent to BODY.PEEK[HEADER],
                   differing in the syntax of the resulting untagged
                   FETCH data (RFC822.HEADER is returned).
    RFC822.SIZE    The [RFC-822] size of the message.
    RFC822.TEXT    Functionally equivalent to BODY[TEXT], differing in
                   the syntax of the resulting untagged FETCH data
                   (RFC822.TEXT is returned).
    UID            The unique identifier for the message.

Crispin Standards Track [Page 44] RFC 2060 IMAP4rev1 December 1996

 Example:    C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)])
             S: * 2 FETCH ....
             S: * 3 FETCH ....
             S: * 4 FETCH ....
             S: A654 OK FETCH completed

6.4.6. STORE Command

 Arguments:  message set
             message data item name
             value for message data item
 Responses:  untagged responses: FETCH
 Result:     OK - store completed
             NO - store error: can't store that data
             BAD - command unknown or arguments invalid
    The STORE command alters data associated with a message in the
    mailbox.  Normally, STORE will return the updated value of the
    data with an untagged FETCH response.  A suffix of ".SILENT" in
    the data item name prevents the untagged FETCH, and the server
    SHOULD assume that the client has determined the updated value
    itself or does not care about the updated value.
       Note: regardless of whether or not the ".SILENT" suffix was
       used, the server SHOULD send an untagged FETCH response if a
       change to a message's flags from an external source is
       observed.  The intent is that the status of the flags is
       determinate without a race condition.
    The currently defined data items that can be stored are:
    FLAGS <flag list>
                   Replace the flags for the message with the
                   argument.  The new value of the flags are returned
                   as if a FETCH of those flags was done.
    FLAGS.SILENT <flag list>
                   Equivalent to FLAGS, but without returning a new
                   value.
    +FLAGS <flag list>
                   Add the argument to the flags for the message.  The
                   new value of the flags are returned as if a FETCH
                   of those flags was done.

Crispin Standards Track [Page 45] RFC 2060 IMAP4rev1 December 1996

    +FLAGS.SILENT <flag list>
                   Equivalent to +FLAGS, but without returning a new
                   value.
  1. FLAGS <flag list>

Remove the argument from the flags for the message.

                   The new value of the flags are returned as if a
                   FETCH of those flags was done.
  1. FLAGS.SILENT <flag list>

Equivalent to -FLAGS, but without returning a new

                   value.
 Example:    C: A003 STORE 2:4 +FLAGS (\Deleted)
             S: * 2 FETCH FLAGS (\Deleted \Seen)
             S: * 3 FETCH FLAGS (\Deleted)
             S: * 4 FETCH FLAGS (\Deleted \Flagged \Seen)
             S: A003 OK STORE completed

6.4.7. COPY Command

 Arguments:  message set
             mailbox name
 Responses:  no specific responses for this command
 Result:     OK - copy completed
             NO - copy error: can't copy those messages or to that
                  name
             BAD - command unknown or arguments invalid
    The COPY command copies the specified message(s) to the end of the
    specified destination mailbox.  The flags and internal date of the
    message(s) SHOULD be preserved in the copy.
    If the destination mailbox does not exist, a server SHOULD return
    an error.  It SHOULD NOT automatically create the mailbox.  Unless
    it is certain that the destination mailbox can not be created, the
    server MUST send the response code "[TRYCREATE]" as the prefix of
    the text of the tagged NO response.  This gives a hint to the
    client that it can attempt a CREATE command and retry the COPY if
    the CREATE is successful.

Crispin Standards Track [Page 46] RFC 2060 IMAP4rev1 December 1996

    If the COPY command is unsuccessful for any reason, server
    implementations MUST restore the destination mailbox to its state
    before the COPY attempt.
 Example:    C: A003 COPY 2:4 MEETING
             S: A003 OK COPY completed

6.4.8. UID Command

 Arguments:  command name
             command arguments
 Responses:  untagged responses: FETCH, SEARCH
 Result:     OK - UID command completed
             NO - UID command error
             BAD - command unknown or arguments invalid
    The UID command has two forms.  In the first form, it takes as its
    arguments a COPY, FETCH, or STORE command with arguments
    appropriate for the associated command.  However, the numbers in
    the message set argument are unique identifiers instead of message
    sequence numbers.
    In the second form, the UID command takes a SEARCH command with
    SEARCH command arguments.  The interpretation of the arguments is
    the same as with SEARCH; however, the numbers returned in a SEARCH
    response for a UID SEARCH command are unique identifiers instead
    of message sequence numbers.  For example, the command UID SEARCH
    1:100 UID 443:557 returns the unique identifiers corresponding to
    the intersection of the message sequence number set 1:100 and the
    UID set 443:557.
    Message set ranges are permitted; however, there is no guarantee
    that unique identifiers be contiguous.  A non-existent unique
    identifier within a message set range is ignored without any error
    message generated.
    The number after the "*" in an untagged FETCH response is always a
    message sequence number, not a unique identifier, even for a UID
    command response.  However, server implementations MUST implicitly
    include the UID message data item as part of any FETCH response
    caused by a UID command, regardless of whether a UID was specified
    as a message data item to the FETCH.

Crispin Standards Track [Page 47] RFC 2060 IMAP4rev1 December 1996

 Example:    C: A999 UID FETCH 4827313:4828442 FLAGS
             S: * 23 FETCH (FLAGS (\Seen) UID 4827313)
             S: * 24 FETCH (FLAGS (\Seen) UID 4827943)
             S: * 25 FETCH (FLAGS (\Seen) UID 4828442)
             S: A999 UID FETCH completed

6.5. Client Commands - Experimental/Expansion

6.5.1. X<atom> Command

 Arguments:  implementation defined
 Responses:  implementation defined
 Result:     OK - command completed
             NO - failure
             BAD - command unknown or arguments invalid
    Any command prefixed with an X is an experimental command.
    Commands which are not part of this specification, a standard or
    standards-track revision of this specification, or an IESG-
    approved experimental protocol, MUST use the X prefix.
    Any added untagged responses issued by an experimental command
    MUST also be prefixed with an X.  Server implementations MUST NOT
    send any such untagged responses, unless the client requested it
    by issuing the associated experimental command.
 Example:    C: a441 CAPABILITY
             S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4 XPIG-LATIN
             S: a441 OK CAPABILITY completed
             C: A442 XPIG-LATIN
             S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay
             S: A442 OK XPIG-LATIN ompleted-cay

7. Server Responses

 Server responses are in three forms: status responses, server data,
 and command continuation request.  The information contained in a
 server response, identified by "Contents:" in the response
 descriptions below, is described by function, not by syntax.  The
 precise syntax of server responses is described in the Formal Syntax
 section.
 The client MUST be prepared to accept any response at all times.

Crispin Standards Track [Page 48] RFC 2060 IMAP4rev1 December 1996

 Status responses can be tagged or untagged.  Tagged status responses
 indicate the completion result (OK, NO, or BAD status) of a client
 command, and have a tag matching the command.
 Some status responses, and all server data, are untagged.  An
 untagged response is indicated by the token "*" instead of a tag.
 Untagged status responses indicate server greeting, or server status
 that does not indicate the completion of a command (for example, an
 impending system shutdown alert).  For historical reasons, untagged
 server data responses are also called "unsolicited data", although
 strictly speaking only unilateral server data is truly "unsolicited".
 Certain server data MUST be recorded by the client when it is
 received; this is noted in the description of that data.  Such data
 conveys critical information which affects the interpretation of all
 subsequent commands and responses (e.g. updates reflecting the
 creation or destruction of messages).
 Other server data SHOULD be recorded for later reference; if the
 client does not need to record the data, or if recording the data has
 no obvious purpose (e.g. a SEARCH response when no SEARCH command is
 in progress), the data SHOULD be ignored.
 An example of unilateral untagged server data occurs when the IMAP
 connection is in selected state.  In selected state, the server
 checks the mailbox for new messages as part of command execution.
 Normally, this is part of the execution of every command; hence, a
 NOOP command suffices to check for new messages.  If new messages are
 found, the server sends untagged EXISTS and RECENT responses
 reflecting the new size of the mailbox.  Server implementations that
 offer multiple simultaneous access to the same mailbox SHOULD also
 send appropriate unilateral untagged FETCH and EXPUNGE responses if
 another agent changes the state of any message flags or expunges any
 messages.
 Command continuation request responses use the token "+" instead of a
 tag.  These responses are sent by the server to indicate acceptance
 of an incomplete client command and readiness for the remainder of
 the command.

7.1. Server Responses - Status Responses

 Status responses are OK, NO, BAD, PREAUTH and BYE.  OK, NO, and BAD
 may be tagged or untagged.  PREAUTH and BYE are always untagged.
 Status responses MAY include an OPTIONAL "response code".  A response
 code consists of data inside square brackets in the form of an atom,
 possibly followed by a space and arguments.  The response code

Crispin Standards Track [Page 49] RFC 2060 IMAP4rev1 December 1996

 contains additional information or status codes for client software
 beyond the OK/NO/BAD condition, and are defined when there is a
 specific action that a client can take based upon the additional
 information.
 The currently defined response codes are:
    ALERT          The human-readable text contains a special alert
                   that MUST be presented to the user in a fashion
                   that calls the user's attention to the message.
    NEWNAME        Followed by a mailbox name and a new mailbox name.
                   A SELECT or EXAMINE is failing because the target
                   mailbox name no longer exists because it was
                   renamed to the new mailbox name.  This is a hint to
                   the client that the operation can succeed if the
                   SELECT or EXAMINE is reissued with the new mailbox
                   name.
    PARSE          The human-readable text represents an error in
                   parsing the [RFC-822] header or [MIME-IMB] headers
                   of a message in the mailbox.
    PERMANENTFLAGS Followed by a parenthesized list of flags,
                   indicates which of the known flags that the client
                   can change permanently.  Any flags that are in the
                   FLAGS untagged response, but not the PERMANENTFLAGS
                   list, can not be set permanently.  If the client
                   attempts to STORE a flag that is not in the
                   PERMANENTFLAGS list, the server will either reject
                   it with a NO reply or store the state for the
                   remainder of the current session only.  The
                   PERMANENTFLAGS list can also include the special
                   flag \*, which indicates that it is possible to
                   create new keywords by attempting to store those
                   flags in the mailbox.
    READ-ONLY      The mailbox is selected read-only, or its access
                   while selected has changed from read-write to
                   read-only.
    READ-WRITE     The mailbox is selected read-write, or its access
                   while selected has changed from read-only to
                   read-write.

Crispin Standards Track [Page 50] RFC 2060 IMAP4rev1 December 1996

    TRYCREATE      An APPEND or COPY attempt is failing because the
                   target mailbox does not exist (as opposed to some
                   other reason).  This is a hint to the client that
                   the operation can succeed if the mailbox is first
                   created by the CREATE command.
    UIDVALIDITY    Followed by a decimal number, indicates the unique
                   identifier validity value.
    UNSEEN         Followed by a decimal number, indicates the number
                   of the first message without the \Seen flag set.
    Additional response codes defined by particular client or server
    implementations SHOULD be prefixed with an "X" until they are
    added to a revision of this protocol.  Client implementations
    SHOULD ignore response codes that they do not recognize.

7.1.1. OK Response

 Contents:   OPTIONAL response code
             human-readable text
    The OK response indicates an information message from the server.
    When tagged, it indicates successful completion of the associated
    command.  The human-readable text MAY be presented to the user as
    an information message.  The untagged form indicates an
    information-only message; the nature of the information MAY be
    indicated by a response code.
    The untagged form is also used as one of three possible greetings
    at connection startup.  It indicates that the connection is not
    yet authenticated and that a LOGIN command is needed.
 Example:    S: * OK IMAP4rev1 server ready
             C: A001 LOGIN fred blurdybloop
             S: * OK [ALERT] System shutdown in 10 minutes
             S: A001 OK LOGIN Completed

7.1.2. NO Response

    Contents:   OPTIONAL response code
                human-readable text
    The NO response indicates an operational error message from the
    server.  When tagged, it indicates unsuccessful completion of the
    associated command.  The untagged form indicates a warning; the
    command can still complete successfully.  The human-readable text
    describes the condition.

Crispin Standards Track [Page 51] RFC 2060 IMAP4rev1 December 1996

 Example:    C: A222 COPY 1:2 owatagusiam
             S: * NO Disk is 98% full, please delete unnecessary data
             S: A222 OK COPY completed
             C: A223 COPY 3:200 blurdybloop
             S: * NO Disk is 98% full, please delete unnecessary data
             S: * NO Disk is 99% full, please delete unnecessary data
             S: A223 NO COPY failed: disk is full

7.1.3. BAD Response

 Contents:   OPTIONAL response code
             human-readable text
    The BAD response indicates an error message from the server.  When
    tagged, it reports a protocol-level error in the client's command;
    the tag indicates the command that caused the error.  The untagged
    form indicates a protocol-level error for which the associated
    command can not be determined; it can also indicate an internal
    server failure.  The human-readable text describes the condition.
 Example:    C: ...very long command line...
             S: * BAD Command line too long
             C: ...empty line...
             S: * BAD Empty command line
             C: A443 EXPUNGE
             S: * BAD Disk crash, attempting salvage to a new disk!
             S: * OK Salvage successful, no data lost
             S: A443 OK Expunge completed

7.1.4. PREAUTH Response

 Contents:   OPTIONAL response code
             human-readable text
    The PREAUTH response is always untagged, and is one of three
    possible greetings at connection startup.  It indicates that the
    connection has already been authenticated by external means and
    thus no LOGIN command is needed.
 Example:    S: * PREAUTH IMAP4rev1 server logged in as Smith

7.1.5. BYE Response

 Contents:   OPTIONAL response code
             human-readable text

Crispin Standards Track [Page 52] RFC 2060 IMAP4rev1 December 1996

    The BYE response is always untagged, and indicates that the server
    is about to close the connection.  The human-readable text MAY be
    displayed to the user in a status report by the client.  The BYE
    response is sent under one of four conditions:
       1) as part of a normal logout sequence.  The server will close
          the connection after sending the tagged OK response to the
          LOGOUT command.
       2) as a panic shutdown announcement.  The server closes the
          connection immediately.
       3) as an announcement of an inactivity autologout.  The server
          closes the connection immediately.
       4) as one of three possible greetings at connection startup,
          indicating that the server is not willing to accept a
          connection from this client.  The server closes the
          connection immediately.
    The difference between a BYE that occurs as part of a normal
    LOGOUT sequence (the first case) and a BYE that occurs because of
    a failure (the other three cases) is that the connection closes
    immediately in the failure case.
 Example:    S: * BYE Autologout; idle for too long

7.2. Server Responses - Server and Mailbox Status

 These responses are always untagged.  This is how server and mailbox
 status data are transmitted from the server to the client.  Many of
 these responses typically result from a command with the same name.

7.2.1. CAPABILITY Response

 Contents:   capability listing
    The CAPABILITY response occurs as a result of a CAPABILITY
    command.  The capability listing contains a space-separated
    listing of capability names that the server supports.  The
    capability listing MUST include the atom "IMAP4rev1".
    A capability name which begins with "AUTH=" indicates that the
    server supports that particular authentication mechanism.

Crispin Standards Track [Page 53] RFC 2060 IMAP4rev1 December 1996

    Other capability names indicate that the server supports an
    extension, revision, or amendment to the IMAP4rev1 protocol.
    Server responses MUST conform to this document until the client
    issues a command that uses the associated capability.
    Capability names MUST either begin with "X" or be standard or
    standards-track IMAP4rev1 extensions, revisions, or amendments
    registered with IANA.  A server MUST NOT offer unregistered or
    non-standard capability names, unless such names are prefixed with
    an "X".
    Client implementations SHOULD NOT require any capability name
    other than "IMAP4rev1", and MUST ignore any unknown capability
    names.
 Example:    S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4 XPIG-LATIN

7.2.2. LIST Response

 Contents:   name attributes
             hierarchy delimiter
             name
    The LIST response occurs as a result of a LIST command.  It
    returns a single name that matches the LIST specification.  There
    can be multiple LIST responses for a single LIST command.
    Four name attributes are defined:
    \Noinferiors   It is not possible for any child levels of
                   hierarchy to exist under this name; no child levels
                   exist now and none can be created in the future.
    \Noselect      It is not possible to use this name as a selectable
                   mailbox.
    \Marked        The mailbox has been marked "interesting" by the
                   server; the mailbox probably contains messages that
                   have been added since the last time the mailbox was
                   selected.
    \Unmarked      The mailbox does not contain any additional
                   messages since the last time the mailbox was
                   selected.
    If it is not feasible for the server to determine whether the
    mailbox is "interesting" or not, or if the name is a \Noselect
    name, the server SHOULD NOT send either \Marked or \Unmarked.

Crispin Standards Track [Page 54] RFC 2060 IMAP4rev1 December 1996

    The hierarchy delimiter is a character used to delimit levels of
    hierarchy in a mailbox name.  A client can use it to create child
    mailboxes, and to search higher or lower levels of naming
    hierarchy.  All children of a top-level hierarchy node MUST use
    the same separator character.  A NIL hierarchy delimiter means
    that no hierarchy exists; the name is a "flat" name.
    The name represents an unambiguous left-to-right hierarchy, and
    MUST be valid for use as a reference in LIST and LSUB commands.
    Unless \Noselect is indicated, the name MUST also be valid as an
          argument for commands, such as SELECT, that accept mailbox
    names.
 Example:    S: * LIST (\Noselect) "/" ~/Mail/foo

7.2.3. LSUB Response

 Contents:   name attributes
             hierarchy delimiter
             name
    The LSUB response occurs as a result of an LSUB command.  It
    returns a single name that matches the LSUB specification.  There
    can be multiple LSUB responses for a single LSUB command.  The
    data is identical in format to the LIST response.
 Example:    S: * LSUB () "." #news.comp.mail.misc

7.2.4 STATUS Response

 Contents:   name
             status parenthesized list
    The STATUS response occurs as a result of an STATUS command.  It
    returns the mailbox name that matches the STATUS specification and
    the requested mailbox status information.
 Example:    S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)

7.2.5. SEARCH Response

 Contents:   zero or more numbers

Crispin Standards Track [Page 55] RFC 2060 IMAP4rev1 December 1996

    The SEARCH response occurs as a result of a SEARCH or UID SEARCH
    command.  The number(s) refer to those messages that match the
    search criteria.  For SEARCH, these are message sequence numbers;
    for UID SEARCH, these are unique identifiers.  Each number is
    delimited by a space.
 Example:    S: * SEARCH 2 3 6

7.2.6. FLAGS Response

 Contents:   flag parenthesized list
    The FLAGS response occurs as a result of a SELECT or EXAMINE
    command.  The flag parenthesized list identifies the flags (at a
    minimum, the system-defined flags) that are applicable for this
    mailbox.  Flags other than the system flags can also exist,
    depending on server implementation.
    The update from the FLAGS response MUST be recorded by the client.
 Example:    S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)

7.3. Server Responses - Mailbox Size

 These responses are always untagged.  This is how changes in the size
 of the mailbox are trasnmitted from the server to the client.
 Immediately following the "*" token is a number that represents a
 message count.

7.3.1. EXISTS Response

 Contents:   none
    The EXISTS response reports the number of messages in the mailbox.
    This response occurs as a result of a SELECT or EXAMINE command,
    and if the size of the mailbox changes (e.g. new mail).
    The update from the EXISTS response MUST be recorded by the
    client.
 Example:    S: * 23 EXISTS

Crispin Standards Track [Page 56] RFC 2060 IMAP4rev1 December 1996

7.3.2. RECENT Response

    Contents:   none
    The RECENT response reports the number of messages with the
    \Recent flag set.  This response occurs as a result of a SELECT or
    EXAMINE command, and if the size of the mailbox changes (e.g. new
    mail).
       Note: It is not guaranteed that the message sequence numbers of
       recent messages will be a contiguous range of the highest n
       messages in the mailbox (where n is the value reported by the
       RECENT response).  Examples of situations in which this is not
       the case are: multiple clients having the same mailbox open
       (the first session to be notified will see it as recent, others
       will probably see it as non-recent), and when the mailbox is
       re-ordered by a non-IMAP agent.
       The only reliable way to identify recent messages is to look at
       message flags to see which have the \Recent flag set, or to do
       a SEARCH RECENT.
       The update from the RECENT response MUST be recorded by the
       client.
 Example:    S: * 5 RECENT

7.4. Server Responses - Message Status

 These responses are always untagged.  This is how message data are
 transmitted from the server to the client, often as a result of a
 command with the same name.  Immediately following the "*" token is a
 number that represents a message sequence number.

7.4.1. EXPUNGE Response

 Contents:   none
    The EXPUNGE response reports that the specified message sequence
    number has been permanently removed from the mailbox.  The message
    sequence number for each successive message in the mailbox is
    immediately decremented by 1, and this decrement is reflected in
    message sequence numbers in subsequent responses (including other
    untagged EXPUNGE responses).
    As a result of the immediate decrement rule, message sequence
    numbers that appear in a set of successive EXPUNGE responses
    depend upon whether the messages are removed starting from lower

Crispin Standards Track [Page 57] RFC 2060 IMAP4rev1 December 1996

    numbers to higher numbers, or from higher numbers to lower
    numbers.  For example, if the last 5 messages in a 9-message
    mailbox are expunged; a "lower to higher" server will send five
    untagged EXPUNGE responses for message sequence number 5, whereas
    a "higher to lower server" will send successive untagged EXPUNGE
    responses for message sequence numbers 9, 8, 7, 6, and 5.
    An EXPUNGE response MUST NOT be sent when no command is in
    progress; nor while responding to a FETCH, STORE, or SEARCH
    command.  This rule is necessary to prevent a loss of
    synchronization of message sequence numbers between client and
    server.
    The update from the EXPUNGE response MUST be recorded by the
    client.
 Example:    S: * 44 EXPUNGE

7.4.2. FETCH Response

 Contents:   message data
    The FETCH response returns data about a message to the client.
    The data are pairs of data item names and their values in
    parentheses.  This response occurs as the result of a FETCH or
    STORE command, as well as by unilateral server decision (e.g. flag
    updates).
    The current data items are:
    BODY           A form of BODYSTRUCTURE without extension data.
    BODY[<section>]<<origin_octet>>
                   A string expressing the body contents of the
                   specified section.  The string SHOULD be
                   interpreted by the client according to the content
                   transfer encoding, body type, and subtype.
                   If the origin octet is specified, this string is a
                   substring of the entire body contents, starting at
                   that origin octet.  This means that BODY[]<0> MAY
                   be truncated, but BODY[] is NEVER truncated.
                   8-bit textual data is permitted if a [CHARSET]
                   identifier is part of the body parameter
                   parenthesized list for this section.  Note that
                   headers (part specifiers HEADER or MIME, or the
                   header portion of a MESSAGE/RFC822 part), MUST be

Crispin Standards Track [Page 58] RFC 2060 IMAP4rev1 December 1996

                   7-bit; 8-bit characters are not permitted in
                   headers.  Note also that the blank line at the end
                   of the header is always included in header data.
                   Non-textual data such as binary data MUST be
                   transfer encoded into a textual form such as BASE64
                   prior to being sent to the client.  To derive the
                   original binary data, the client MUST decode the
                   transfer encoded string.
    BODYSTRUCTURE  A parenthesized list that describes the [MIME-IMB]
                   body structure of a message.  This is computed by
                   the server by parsing the [MIME-IMB] header fields,
                   defaulting various fields as necessary.
                   For example, a simple text message of 48 lines and
                   2279 octets can have a body structure of: ("TEXT"
                   "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 2279
                   48)
                   Multiple parts are indicated by parenthesis
                   nesting.  Instead of a body type as the first
                   element of the parenthesized list there is a nested
                   body.  The second element of the parenthesized list
                   is the multipart subtype (mixed, digest, parallel,
                   alternative, etc.).
                   For example, a two part message consisting of a
                   text and a BASE645-encoded text attachment can have
                   a body structure of: (("TEXT" "PLAIN" ("CHARSET"
                   "US-ASCII") NIL NIL "7BIT" 1152 23)("TEXT" "PLAIN"
                   ("CHARSET" "US-ASCII" "NAME" "cc.diff")
                   "<960723163407.20117h@cac.washington.edu>"
                   "Compiler diff" "BASE64" 4554 73) "MIXED"))
                   Extension data follows the multipart subtype.
                   Extension data is never returned with the BODY
                   fetch, but can be returned with a BODYSTRUCTURE
                   fetch.  Extension data, if present, MUST be in the
                   defined order.
                   The extension data of a multipart body part are in
                   the following order:
                   body parameter parenthesized list
                      A parenthesized list of attribute/value pairs
                      [e.g. ("foo" "bar" "baz" "rag") where "bar" is
                      the value of "foo" and "rag" is the value of

Crispin Standards Track [Page 59] RFC 2060 IMAP4rev1 December 1996

                      "baz"] as defined in [MIME-IMB].
                   body disposition
                      A parenthesized list, consisting of a
                      disposition type string followed by a
                      parenthesized list of disposition
                      attribute/value pairs.  The disposition type and
                      attribute names will be defined in a future
                      standards-track revision to [DISPOSITION].
                   body language
                      A string or parenthesized list giving the body
                      language value as defined in [LANGUAGE-TAGS].
                   Any following extension data are not yet defined in
                   this version of the protocol.  Such extension data
                   can consist of zero or more NILs, strings, numbers,
                   or potentially nested parenthesized lists of such
                   data.  Client implementations that do a
                   BODYSTRUCTURE fetch MUST be prepared to accept such
                   extension data.  Server implementations MUST NOT
                   send such extension data until it has been defined
                   by a revision of this protocol.
                   The basic fields of a non-multipart body part are
                   in the following order:
                   body type
                      A string giving the content media type name as
                      defined in [MIME-IMB].
                   body subtype
                      A string giving the content subtype name as
                      defined in [MIME-IMB].
                   body parameter parenthesized list
                      A parenthesized list of attribute/value pairs
                      [e.g. ("foo" "bar" "baz" "rag") where "bar" is
                      the value of "foo" and "rag" is the value of
                      "baz"] as defined in [MIME-IMB].
                   body id
                      A string giving the content id as defined in
                      [MIME-IMB].
                   body description
                      A string giving the content description as
                      defined in [MIME-IMB].

Crispin Standards Track [Page 60] RFC 2060 IMAP4rev1 December 1996

                   body encoding
                      A string giving the content transfer encoding as
                      defined in [MIME-IMB].
                   body size
                      A number giving the size of the body in octets.
                      Note that this size is the size in its transfer
                      encoding and not the resulting size after any
                      decoding.
                   A body type of type MESSAGE and subtype RFC822
                   contains, immediately after the basic fields, the
                   envelope structure, body structure, and size in
                   text lines of the encapsulated message.
                   A body type of type TEXT contains, immediately
                   after the basic fields, the size of the body in
                   text lines.  Note that this size is the size in its
                   content transfer encoding and not the resulting
                   size after any decoding.
                   Extension data follows the basic fields and the
                   type-specific fields listed above.  Extension data
                   is never returned with the BODY fetch, but can be
                   returned with a BODYSTRUCTURE fetch.  Extension
                   data, if present, MUST be in the defined order.
                   The extension data of a non-multipart body part are
                   in the following order:
                   body MD5
                      A string giving the body MD5 value as defined in
                      [MD5].
                   body disposition
                      A parenthesized list with the same content and
                      function as the body disposition for a multipart
                      body part.
                   body language
                      A string or parenthesized list giving the body
                      language value as defined in [LANGUAGE-TAGS].
                   Any following extension data are not yet defined in
                   this version of the protocol, and would be as
                   described above under multipart extension data.

Crispin Standards Track [Page 61] RFC 2060 IMAP4rev1 December 1996

    ENVELOPE       A parenthesized list that describes the envelope
                   structure of a message.  This is computed by the
                   server by parsing the [RFC-822] header into the
                   component parts, defaulting various fields as
                   necessary.
                   The fields of the envelope structure are in the
                   following order: date, subject, from, sender,
                   reply-to, to, cc, bcc, in-reply-to, and message-id.
                   The date, subject, in-reply-to, and message-id
                   fields are strings.  The from, sender, reply-to,
                   to, cc, and bcc fields are parenthesized lists of
                   address structures.
                   An address structure is a parenthesized list that
                   describes an electronic mail address.  The fields
                   of an address structure are in the following order:
                   personal name, [SMTP] at-domain-list (source
                   route), mailbox name, and host name.
                   [RFC-822] group syntax is indicated by a special
                   form of address structure in which the host name
                   field is NIL.  If the mailbox name field is also
                   NIL, this is an end of group marker (semi-colon in
                   RFC 822 syntax).  If the mailbox name field is
                   non-NIL, this is a start of group marker, and the
                   mailbox name field holds the group name phrase.
                   Any field of an envelope or address structure that
                   is not applicable is presented as NIL.  Note that
                   the server MUST default the reply-to and sender
                   fields from the from field; a client is not
                   expected to know to do this.
    FLAGS          A parenthesized list of flags that are set for this
                   message.
    INTERNALDATE   A string representing the internal date of the
                   message.
    RFC822         Equivalent to BODY[].
    RFC822.HEADER  Equivalent to BODY.PEEK[HEADER].
    RFC822.SIZE    A number expressing the [RFC-822] size of the
                   message.
    RFC822.TEXT    Equivalent to BODY[TEXT].

Crispin Standards Track [Page 62] RFC 2060 IMAP4rev1 December 1996

    UID            A number expressing the unique identifier of the
                   message.
 Example:    S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)

7.5. Server Responses - Command Continuation Request

 The command continuation request response is indicated by a "+" token
 instead of a tag.  This form of response indicates that the server is
 ready to accept the continuation of a command from the client.  The
 remainder of this response is a line of text.
 This response is used in the AUTHORIZATION command to transmit server
 data to the client, and request additional client data.  This
 response is also used if an argument to any command is a literal.
 The client is not permitted to send the octets of the literal unless
 the server indicates that it expects it.  This permits the server to
 process commands and reject errors on a line-by-line basis.  The
 remainder of the command, including the CRLF that terminates a
 command, follows the octets of the literal.  If there are any
 additional command arguments the literal octets are followed by a
 space and those arguments.
 Example:    C: A001 LOGIN {11}
             S: + Ready for additional command text
             C: FRED FOOBAR {7}
             S: + Ready for additional command text
             C: fat man
             S: A001 OK LOGIN completed
             C: A044 BLURDYBLOOP {102856}
             S: A044 BAD No such command as "BLURDYBLOOP"

8. Sample IMAP4rev1 connection

 The following is a transcript of an IMAP4rev1 connection.  A long
 line in this sample is broken for editorial clarity.

S: * OK IMAP4rev1 Service Ready C: a001 login mrc secret S: a001 OK LOGIN completed C: a002 select inbox S: * 18 EXISTS S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * 2 RECENT S: * OK [UNSEEN 17] Message 17 is the first unseen message S: * OK [UIDVALIDITY 3857529045] UIDs valid

Crispin Standards Track [Page 63] RFC 2060 IMAP4rev1 December 1996

S: a002 OK [READ-WRITE] SELECT completed C: a003 fetch 12 full S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700"

    RFC822.SIZE 4286 ENVELOPE ("Wed, 17 Jul 1996 02:23:25 -0700 (PDT)"
    "IMAP4rev1 WG mtg summary and minutes"
    (("Terry Gray" NIL "gray" "cac.washington.edu"))
    (("Terry Gray" NIL "gray" "cac.washington.edu"))
    (("Terry Gray" NIL "gray" "cac.washington.edu"))
    ((NIL NIL "imap" "cac.washington.edu"))
    ((NIL NIL "minutes" "CNRI.Reston.VA.US")
    ("John Klensin" NIL "KLENSIN" "INFOODS.MIT.EDU")) NIL NIL
    "<B27397-0100000@cac.washington.edu>")
     BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028 92))

S: a003 OK FETCH completed C: a004 fetch 12 body[header] S: * 12 FETCH (BODY[HEADER] {350} S: Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT) S: From: Terry Gray gray@cac.washington.edu S: Subject: IMAP4rev1 WG mtg summary and minutes S: To: imap@cac.washington.edu S: cc: minutes@CNRI.Reston.VA.US, John Klensin KLENSIN@INFOODS.MIT.EDU S: Message-Id: B27397-0100000@cac.washington.edu S: MIME-Version: 1.0 S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII S: S: ) S: a004 OK FETCH completed C: a005 store 12 +flags \deleted S: * 12 FETCH (FLAGS (\Seen \Deleted)) S: a005 OK +FLAGS completed C: a006 logout S: * BYE IMAP4rev1 server terminating connection S: a006 OK LOGOUT completed

9. Formal Syntax

 The following syntax specification uses the augmented Backus-Naur
 Form (BNF) notation as specified in [RFC-822] with one exception; the
 delimiter used with the "#" construct is a single space (SPACE) and
 not one or more commas.
 In the case of alternative or optional rules in which a later rule
 overlaps an earlier rule, the rule which is listed earlier MUST take
 priority.  For example, "\Seen" when parsed as a flag is the \Seen
 flag name and not a flag_extension, even though "\Seen" could be
 parsed as a flag_extension.  Some, but not all, instances of this
 rule are noted below.

Crispin Standards Track [Page 64] RFC 2060 IMAP4rev1 December 1996

 Except as noted otherwise, all alphabetic characters are case-
 insensitive.  The use of upper or lower case characters to define
 token strings is for editorial clarity only.  Implementations MUST
 accept these strings in a case-insensitive fashion.

address ::= "(" addr_name SPACE addr_adl SPACE addr_mailbox

                  SPACE addr_host ")"

addr_adl ::= nstring

                  ;; Holds route from [RFC-822] route-addr if
                  ;; non-NIL

addr_host ::= nstring

                  ;; NIL indicates [RFC-822] group syntax.
                  ;; Otherwise, holds [RFC-822] domain name

addr_mailbox ::= nstring

                  ;; NIL indicates end of [RFC-822] group; if
                  ;; non-NIL and addr_host is NIL, holds
                  ;; [RFC-822] group name.
                  ;; Otherwise, holds [RFC-822] local-part

addr_name ::= nstring

                  ;; Holds phrase from [RFC-822] mailbox if
                  ;; non-NIL

alpha ::= "A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" /

                  "I" / "J" / "K" / "L" / "M" / "N" / "O" / "P" /
                  "Q" / "R" / "S" / "T" / "U" / "V" / "W" / "X" /
                  "Y" / "Z" /
                  "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" /
                  "i" / "j" / "k" / "l" / "m" / "n" / "o" / "p" /
                  "q" / "r" / "s" / "t" / "u" / "v" / "w" / "x" /
                  "y" / "z"
                  ;; Case-sensitive

append ::= "APPEND" SPACE mailbox [SPACE flag_list]

                  [SPACE date_time] SPACE literal

astring ::= atom / string

atom ::= 1*ATOM_CHAR

ATOM_CHAR ::= <any CHAR except atom_specials>

atom_specials ::= "(" / ")" / "{" / SPACE / CTL / list_wildcards /

                  quoted_specials

Crispin Standards Track [Page 65] RFC 2060 IMAP4rev1 December 1996

authenticate ::= "AUTHENTICATE" SPACE auth_type *(CRLF base64)

auth_type ::= atom

                  ;; Defined by [IMAP-AUTH]

base64 ::= *(4base64_char) [base64_terminal]

base64_char ::= alpha / digit / "+" / "/"

base64_terminal ::= (2base64_char "==") / (3base64_char "=")

body ::= "(" body_type_1part / body_type_mpart ")"

body_extension ::= nstring / number / "(" 1#body_extension ")"

                  ;; Future expansion.  Client implementations
                  ;; MUST accept body_extension fields.  Server
                  ;; implementations MUST NOT generate
                  ;; body_extension fields except as defined by
                  ;; future standard or standards-track
                  ;; revisions of this specification.

body_ext_1part ::= body_fld_md5 [SPACE body_fld_dsp

                  [SPACE body_fld_lang
                  [SPACE 1#body_extension]]]
                  ;; MUST NOT be returned on non-extensible
                  ;; "BODY" fetch

body_ext_mpart ::= body_fld_param

                  [SPACE body_fld_dsp SPACE body_fld_lang
                  [SPACE 1#body_extension]]
                  ;; MUST NOT be returned on non-extensible
                  ;; "BODY" fetch

body_fields ::= body_fld_param SPACE body_fld_id SPACE

                  body_fld_desc SPACE body_fld_enc SPACE
                  body_fld_octets

body_fld_desc ::= nstring

body_fld_dsp ::= "(" string SPACE body_fld_param ")" / nil

body_fld_enc ::= (<"> ("7BIT" / "8BIT" / "BINARY" / "BASE64"/

                  "QUOTED-PRINTABLE") <">) / string

body_fld_id ::= nstring

body_fld_lang ::= nstring / "(" 1#string ")"

Crispin Standards Track [Page 66] RFC 2060 IMAP4rev1 December 1996

body_fld_lines ::= number

body_fld_md5 ::= nstring

body_fld_octets ::= number

body_fld_param ::= "(" 1#(string SPACE string) ")" / nil

body_type_1part ::= (body_type_basic / body_type_msg / body_type_text)

                  [SPACE body_ext_1part]

body_type_basic ::= media_basic SPACE body_fields

                  ;; MESSAGE subtype MUST NOT be "RFC822"

body_type_mpart ::= 1*body SPACE media_subtype

                  [SPACE body_ext_mpart]

body_type_msg ::= media_message SPACE body_fields SPACE envelope

                  SPACE body SPACE body_fld_lines

body_type_text ::= media_text SPACE body_fields SPACE body_fld_lines

capability ::= "AUTH=" auth_type / atom

                  ;; New capabilities MUST begin with "X" or be
                  ;; registered with IANA as standard or
                  ;; standards-track

capability_data ::= "CAPABILITY" SPACE [1#capability SPACE] "IMAP4rev1"

                  [SPACE 1#capability]
                  ;; IMAP4rev1 servers which offer RFC 1730
                  ;; compatibility MUST list "IMAP4" as the first
                  ;; capability.

CHAR ::= <any 7-bit US-ASCII character except NUL,

                   0x01 - 0x7f>

CHAR8 ::= <any 8-bit octet except NUL, 0x01 - 0xff>

command ::= tag SPACE (command_any / command_auth /

                  command_nonauth / command_select) CRLF
                  ;; Modal based on state

command_any ::= "CAPABILITY" / "LOGOUT" / "NOOP" / x_command

                  ;; Valid in all states

command_auth ::= append / create / delete / examine / list / lsub /

                  rename / select / status / subscribe / unsubscribe
                  ;; Valid only in Authenticated or Selected state

Crispin Standards Track [Page 67] RFC 2060 IMAP4rev1 December 1996

command_nonauth ::= login / authenticate

                  ;; Valid only when in Non-Authenticated state

command_select ::= "CHECK" / "CLOSE" / "EXPUNGE" /

                   copy / fetch / store / uid / search
                  ;; Valid only when in Selected state

continue_req ::= "+" SPACE (resp_text / base64)

copy ::= "COPY" SPACE set SPACE mailbox

CR ::= <ASCII CR, carriage return, 0x0D>

create ::= "CREATE" SPACE mailbox

                  ;; Use of INBOX gives a NO error

CRLF ::= CR LF

CTL ::= <any ASCII control character and DEL,

                      0x00 - 0x1f, 0x7f>

date ::= date_text / <"> date_text <">

date_day ::= 1*2digit

                  ;; Day of month

date_day_fixed ::= (SPACE digit) / 2digit

                  ;; Fixed-format version of date_day

date_month ::= "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" /

                  "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"

date_text ::= date_day "-" date_month "-" date_year

date_year ::= 4digit

date_time ::= <"> date_day_fixed "-" date_month "-" date_year

                  SPACE time SPACE zone <">

delete ::= "DELETE" SPACE mailbox

                  ;; Use of INBOX gives a NO error

digit ::= "0" / digit_nz

digit_nz ::= "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" /

                  "9"

Crispin Standards Track [Page 68] RFC 2060 IMAP4rev1 December 1996

envelope ::= "(" env_date SPACE env_subject SPACE env_from

                  SPACE env_sender SPACE env_reply_to SPACE env_to
                  SPACE env_cc SPACE env_bcc SPACE env_in_reply_to
                  SPACE env_message_id ")"

env_bcc ::= "(" 1*address ")" / nil

env_cc ::= "(" 1*address ")" / nil

env_date ::= nstring

env_from ::= "(" 1*address ")" / nil

env_in_reply_to ::= nstring

env_message_id ::= nstring

env_reply_to ::= "(" 1*address ")" / nil

env_sender ::= "(" 1*address ")" / nil

env_subject ::= nstring

env_to ::= "(" 1*address ")" / nil

examine ::= "EXAMINE" SPACE mailbox

fetch ::= "FETCH" SPACE set SPACE ("ALL" / "FULL" /

                  "FAST" / fetch_att / "(" 1#fetch_att ")")

fetch_att ::= "ENVELOPE" / "FLAGS" / "INTERNALDATE" /

                  "RFC822" [".HEADER" / ".SIZE" / ".TEXT"] /
                  "BODY" ["STRUCTURE"] / "UID" /
                  "BODY" [".PEEK"] section
                  ["<" number "." nz_number ">"]

flag ::= "\Answered" / "\Flagged" / "\Deleted" /

                  "\Seen" / "\Draft" / flag_keyword / flag_extension

flag_extension ::= "\" atom

                  ;; Future expansion.  Client implementations
                  ;; MUST accept flag_extension flags.  Server
                  ;; implementations MUST NOT generate
                  ;; flag_extension flags except as defined by
                  ;; future standard or standards-track
                  ;; revisions of this specification.

flag_keyword ::= atom

Crispin Standards Track [Page 69] RFC 2060 IMAP4rev1 December 1996

flag_list ::= "(" #flag ")"

greeting ::= "*" SPACE (resp_cond_auth / resp_cond_bye) CRLF

header_fld_name ::= astring

header_list ::= "(" 1#header_fld_name ")"

LF ::= <ASCII LF, line feed, 0x0A>

list ::= "LIST" SPACE mailbox SPACE list_mailbox

list_mailbox ::= 1*(ATOM_CHAR / list_wildcards) / string

list_wildcards ::= "%" / "*"

literal ::= "{" number "}" CRLF *CHAR8

                  ;; Number represents the number of CHAR8 octets

login ::= "LOGIN" SPACE userid SPACE password

lsub ::= "LSUB" SPACE mailbox SPACE list_mailbox

mailbox ::= "INBOX" / astring

                  ;; INBOX is case-insensitive.  All case variants of
                  ;; INBOX (e.g. "iNbOx") MUST be interpreted as INBOX
                  ;; not as an astring.  Refer to section 5.1 for
                  ;; further semantic details of mailbox names.

mailbox_data ::= "FLAGS" SPACE flag_list /

                   "LIST" SPACE mailbox_list /
                   "LSUB" SPACE mailbox_list /
                   "MAILBOX" SPACE text /
                   "SEARCH" [SPACE 1#nz_number] /
                   "STATUS" SPACE mailbox SPACE
                   "(" #<status_att number ")" /
                   number SPACE "EXISTS" / number SPACE "RECENT"

mailbox_list ::= "(" #("\Marked" / "\Noinferiors" /

                  "\Noselect" / "\Unmarked" / flag_extension) ")"
                  SPACE (<"> QUOTED_CHAR <"> / nil) SPACE mailbox

media_basic ::= (<"> ("APPLICATION" / "AUDIO" / "IMAGE" /

                  "MESSAGE" / "VIDEO") <">) / string)
                  SPACE media_subtype
                  ;; Defined in [MIME-IMT]

media_message ::= <"> "MESSAGE" <"> SPACE <"> "RFC822" <">

Crispin Standards Track [Page 70] RFC 2060 IMAP4rev1 December 1996

                  ;; Defined in [MIME-IMT]

media_subtype ::= string

                  ;; Defined in [MIME-IMT]

media_text ::= <"> "TEXT" <"> SPACE media_subtype

                  ;; Defined in [MIME-IMT]

message_data ::= nz_number SPACE ("EXPUNGE" /

                                  ("FETCH" SPACE msg_att))

msg_att ::= "(" 1#("ENVELOPE" SPACE envelope /

                  "FLAGS" SPACE "(" #(flag / "\Recent") ")" /
                  "INTERNALDATE" SPACE date_time /
                  "RFC822" [".HEADER" / ".TEXT"] SPACE nstring /
                  "RFC822.SIZE" SPACE number /
                  "BODY" ["STRUCTURE"] SPACE body /
                  "BODY" section ["<" number ">"] SPACE nstring /
                  "UID" SPACE uniqueid) ")"

nil ::= "NIL"

nstring ::= string / nil

number ::= 1*digit

                  ;; Unsigned 32-bit integer
                  ;; (0 <= n < 4,294,967,296)

nz_number ::= digit_nz *digit

                  ;; Non-zero unsigned 32-bit integer
                  ;; (0 < n < 4,294,967,296)

password ::= astring

quoted ::= <"> *QUOTED_CHAR <">

QUOTED_CHAR ::= <any TEXT_CHAR except quoted_specials> /

                  "\" quoted_specials

quoted_specials ::= <"> / "\"

rename ::= "RENAME" SPACE mailbox SPACE mailbox

                  ;; Use of INBOX as a destination gives a NO error

response ::= *(continue_req / response_data) response_done

response_data ::= "*" SPACE (resp_cond_state / resp_cond_bye /

                  mailbox_data / message_data / capability_data)

Crispin Standards Track [Page 71] RFC 2060 IMAP4rev1 December 1996

                  CRLF

response_done ::= response_tagged / response_fatal

response_fatal ::= "*" SPACE resp_cond_bye CRLF

                  ;; Server closes connection immediately

response_tagged ::= tag SPACE resp_cond_state CRLF

resp_cond_auth ::= ("OK" / "PREAUTH") SPACE resp_text

                  ;; Authentication condition

resp_cond_bye ::= "BYE" SPACE resp_text

resp_cond_state ::= ("OK" / "NO" / "BAD") SPACE resp_text

                  ;; Status condition

resp_text ::= ["[" resp_text_code "]" SPACE] (text_mime2 / text)

                  ;; text SHOULD NOT begin with "[" or "="

resp_text_code ::= "ALERT" / "PARSE" /

                  "PERMANENTFLAGS" SPACE "(" #(flag / "\*") ")" /
                  "READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
                  "UIDVALIDITY" SPACE nz_number /
                  "UNSEEN" SPACE nz_number /
                  atom [SPACE 1*<any TEXT_CHAR except "]">]

search ::= "SEARCH" SPACE ["CHARSET" SPACE astring SPACE]

                  1#search_key
                  ;; [CHARSET] MUST be registered with IANA

search_key ::= "ALL" / "ANSWERED" / "BCC" SPACE astring /

                  "BEFORE" SPACE date / "BODY" SPACE astring /
                  "CC" SPACE astring / "DELETED" / "FLAGGED" /
                  "FROM" SPACE astring /
                  "KEYWORD" SPACE flag_keyword / "NEW" / "OLD" /
                  "ON" SPACE date / "RECENT" / "SEEN" /
                  "SINCE" SPACE date / "SUBJECT" SPACE astring /
                  "TEXT" SPACE astring / "TO" SPACE astring /
                  "UNANSWERED" / "UNDELETED" / "UNFLAGGED" /
                  "UNKEYWORD" SPACE flag_keyword / "UNSEEN" /
                  ;; Above this line were in [IMAP2]
                  "DRAFT" /
                  "HEADER" SPACE header_fld_name SPACE astring /
                  "LARGER" SPACE number / "NOT" SPACE search_key /
                  "OR" SPACE search_key SPACE search_key /
                  "SENTBEFORE" SPACE date / "SENTON" SPACE date /
                  "SENTSINCE" SPACE date / "SMALLER" SPACE number /

Crispin Standards Track [Page 72] RFC 2060 IMAP4rev1 December 1996

                  "UID" SPACE set / "UNDRAFT" / set /
                  "(" 1#search_key ")"

section ::= "[" [section_text / (nz_number *["." nz_number]

                  ["." (section_text / "MIME")])] "]"

section_text ::= "HEADER" / "HEADER.FIELDS" [".NOT"]

                  SPACE header_list / "TEXT"

select ::= "SELECT" SPACE mailbox

sequence_num ::= nz_number / "*"

                  ;; * is the largest number in use.  For message
                  ;; sequence numbers, it is the number of messages
                  ;; in the mailbox.  For unique identifiers, it is
                  ;; the unique identifier of the last message in
                  ;; the mailbox.

set ::= sequence_num / (sequence_num ":" sequence_num) /

                  (set "," set)
                  ;; Identifies a set of messages.  For message
                  ;; sequence numbers, these are consecutive
                  ;; numbers from 1 to the number of messages in
                  ;; the mailbox
                  ;; Comma delimits individual numbers, colon
                  ;; delimits between two numbers inclusive.
                  ;; Example: 2,4:7,9,12:* is 2,4,5,6,7,9,12,13,
                  ;; 14,15 for a mailbox with 15 messages.

SPACE ::= <ASCII SP, space, 0x20>

status ::= "STATUS" SPACE mailbox SPACE "(" 1#status_att ")"

status_att ::= "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" /

                  "UNSEEN"

store ::= "STORE" SPACE set SPACE store_att_flags

store_att_flags ::= (["+" / "-"] "FLAGS" [".SILENT"]) SPACE

                  (flag_list / #flag)

string ::= quoted / literal

subscribe ::= "SUBSCRIBE" SPACE mailbox

tag ::= 1*<any ATOM_CHAR except "+">

text ::= 1*TEXT_CHAR

Crispin Standards Track [Page 73] RFC 2060 IMAP4rev1 December 1996

text_mime2 ::= "=?" <charset> "?" <encoding> "?"

                   <encoded-text> "?="
                   ;; Syntax defined in [MIME-HDRS]

TEXT_CHAR ::= <any CHAR except CR and LF>

time ::= 2digit ":" 2digit ":" 2digit

                  ;; Hours minutes seconds

uid ::= "UID" SPACE (copy / fetch / search / store)

                  ;; Unique identifiers used instead of message
                  ;; sequence numbers

uniqueid ::= nz_number

                  ;; Strictly ascending

unsubscribe ::= "UNSUBSCRIBE" SPACE mailbox

userid ::= astring

x_command ::= "X" atom <experimental command arguments>

zone ::= ("+" / "-") 4digit

                  ;; Signed four-digit value of hhmm representing
                  ;; hours and minutes west of Greenwich (that is,
                  ;; (the amount that the given time differs from
                  ;; Universal Time).  Subtracting the timezone
                  ;; from the given time will give the UT form.
                  ;; The Universal Time zone is "+0000".

10. Author's Note

 This document is a revision or rewrite of earlier documents, and
 supercedes the protocol specification in those documents: RFC 1730,
 unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.

11. Security Considerations

 IMAP4rev1 protocol transactions, including electronic mail data, are
 sent in the clear over the network unless privacy protection is
 negotiated in the AUTHENTICATE command.
 A server error message for an AUTHENTICATE command which fails due to
 invalid credentials SHOULD NOT detail why the credentials are
 invalid.
 Use of the LOGIN command sends passwords in the clear.  This can be
 avoided by using the AUTHENTICATE command instead.

Crispin Standards Track [Page 74] RFC 2060 IMAP4rev1 December 1996

 A server error message for a failing LOGIN command SHOULD NOT specify
 that the user name, as opposed to the password, is invalid.
 Additional security considerations are discussed in the section
 discussing the AUTHENTICATE and LOGIN commands.

12. Author's Address

 Mark R. Crispin
 Networks and Distributed Computing
 University of Washington
 4545 15th Aveneue NE
 Seattle, WA  98105-4527
 Phone: (206) 543-5762
 EMail: MRC@CAC.Washington.EDU

Crispin Standards Track [Page 75] RFC 2060 IMAP4rev1 December 1996

Appendices

A. References

[ACAP] Myers, J. "ACAP – Application Configuration Access Protocol", Work in Progress.

[CHARSET] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700, USC/Information Sciences Institute, October 1994.

[DISPOSITION] Troost, R., and Dorner, S., "Communicating Presentation Information in Internet Messages: The Content-Disposition Header", RFC 1806, June 1995.

[IMAP-AUTH] Myers, J., "IMAP4 Authentication Mechanism", RFC 1731. Carnegie-Mellon University, December 1994.

[IMAP-COMPAT] Crispin, M., "IMAP4 Compatibility with IMAP2bis", RFC 2061, University of Washington, November 1996.

[IMAP-DISC] Austein, R., "Synchronization Operations for Disconnected IMAP4 Clients", Work in Progress.

[IMAP-HISTORICAL] Crispin, M. "IMAP4 Compatibility with IMAP2 and IMAP2bis", RFC 1732, University of Washington, December 1994.

[IMAP-MODEL] Crispin, M., "Distributed Electronic Mail Models in IMAP4", RFC 1733, University of Washington, December 1994.

[IMAP-OBSOLETE] Crispin, M., "Internet Message Access Protocol - Obsolete Syntax", RFC 2062, University of Washington, November 1996.

[IMAP2] Crispin, M., "Interactive Mail Access Protocol - Version 2", RFC 1176, University of Washington, August 1990.

[LANGUAGE-TAGS] Alvestrand, H., "Tags for the Identification of Languages", RFC 1766, March 1995.

[MD5] Myers, J., and M. Rose, "The Content-MD5 Header Field", RFC 1864, October 1995.

[MIME-IMB] Freed, N., and N. Borenstein, "MIME (Multipurpose Internet Mail Extensions) Part One: Format of Internet Message Bodies", RFC 2045, November 1996.

[MIME-IMT] Freed, N., and N. Borenstein, "MIME (Multipurpose Internet Mail Extensions) Part Two: Media Types", RFC 2046, November 1996.

Crispin Standards Track [Page 76] RFC 2060 IMAP4rev1 December 1996

[MIME-HDRS] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996.

[RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, University of Delaware, August 1982.

[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, USC/Information Sciences Institute, August 1982.

[UTF-7] Goldsmith, D., and Davis, M., "UTF-7: A Mail-Safe Transformation Format of Unicode", RFC 1642, July 1994.

B. Changes from RFC 1730

1) The STATUS command has been added.

2) Clarify in the formal syntax that the "#" construct can never refer to multiple spaces.

3) Obsolete syntax has been moved to a separate document.

4) The PARTIAL command has been obsoleted.

5) The RFC822.HEADER.LINES, RFC822.HEADER.LINES.NOT, RFC822.PEEK, and RFC822.TEXT.PEEK fetch attributes have been obsoleted.

6) The "<" origin "." size ">" suffix for BODY text attributes has been added.

7) The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, MIME, and TEXT part specifiers have been added.

8) Support for Content-Disposition and Content-Language has been added.

9) The restriction on fetching nested MULTIPART parts has been removed.

10) Body part number 0 has been obsoleted.

11) Server-supported authenticators are now identified by capabilities.

Crispin Standards Track [Page 77] RFC 2060 IMAP4rev1 December 1996

12) The capability that identifies this protocol is now called "IMAP4rev1". A server that provides backwards support for RFC 1730 SHOULD emit the "IMAP4" capability in addition to "IMAP4rev1" in its CAPABILITY response. Because RFC-1730 required "IMAP4" to appear as the first capability, it MUST listed first in the response.

13) A description of the mailbox name namespace convention has been added.

14) A description of the international mailbox name convention has been added.

15) The UID-NEXT and UID-VALIDITY status items are now called UIDNEXT and UIDVALIDITY. This is a change from the IMAP STATUS Work in Progress and not from RFC-1730

16) Add a clarification that a null mailbox name argument to the LIST command returns an untagged LIST response with the hierarchy delimiter and root of the reference argument.

17) Define terms such as "MUST", "SHOULD", and "MUST NOT".

18) Add a section which defines message attributes and more thoroughly details the semantics of message sequence numbers, UIDs, and flags.

19) Add a clarification detailing the circumstances when a client may send multiple commands without waiting for a response, and the circumstances in which ambiguities may result.

20) Add a recommendation on server behavior for DELETE and RENAME when inferior hierarchical names of the given name exist.

21) Add a clarification that a mailbox name may not be unilaterally unsubscribed by the server, even if that mailbox name no longer exists.

22) Add a clarification that LIST should return its results quickly without undue delay.

23) Add a clarification that the date_time argument to APPEND sets the internal date of the message.

24) Add a clarification on APPEND behavior when the target mailbox is the currently selected mailbox.

Crispin Standards Track [Page 78] RFC 2060 IMAP4rev1 December 1996

25) Add a clarification that external changes to flags should be always announced via an untagged FETCH even if the current command is a STORE with the ".SILENT" suffix.

26) Add a clarification that COPY appends to the target mailbox.

27) Add the NEWNAME response code.

28) Rewrite the description of the untagged BYE response to clarify its semantics.

29) Change the reference for the body MD5 to refer to the proper RFC.

30) Clarify that the formal syntax contains rules which may overlap, and that in the event of such an overlap the rule which occurs first takes precedence.

31) Correct the definition of body_fld_param.

32) More formal syntax for capability_data.

33) Clarify that any case variant of "INBOX" must be interpreted as INBOX.

34) Clarify that the human-readable text in resp_text should not begin with "[" or "=".

35) Change MIME references to Draft Standard documents.

36) Clarify \Recent semantics.

37) Additional examples.

C. Key Word Index

     +FLAGS <flag list> (store command data item) ...............   45
     +FLAGS.SILENT <flag list> (store command data item) ........   46
     -FLAGS <flag list> (store command data item) ...............   46
     -FLAGS.SILENT <flag list> (store command data item) ........   46
     ALERT (response code) ......................................   50
     ALL (fetch item) ...........................................   41
     ALL (search key) ...........................................   38
     ANSWERED (search key) ......................................   38
     APPEND (command) ...........................................   34
     AUTHENTICATE (command) .....................................   20
     BAD (response) .............................................   52
     BCC <string> (search key) ..................................   38
     BEFORE <date> (search key) .................................   39

Crispin Standards Track [Page 79] RFC 2060 IMAP4rev1 December 1996

     BODY (fetch item) ..........................................   41
     BODY (fetch result) ........................................   58
     BODY <string> (search key) .................................   39
     BODY.PEEK[<section>]<<partial>> (fetch item) ...............   44
     BODYSTRUCTURE (fetch item) .................................   44
     BODYSTRUCTURE (fetch result) ...............................   59
     BODY[<section>]<<origin_octet>> (fetch result) .............   58
     BODY[<section>]<<partial>> (fetch item) ....................   41
     BYE (response) .............................................   52
     Body Structure (message attribute) .........................   11
     CAPABILITY (command) .......................................   18
     CAPABILITY (response) ......................................   53
     CC <string> (search key) ...................................   39
     CHECK (command) ............................................   36
     CLOSE (command) ............................................   36
     COPY (command) .............................................   46
     CREATE (command) ...........................................   25
     DELETE (command) ...........................................   26
     DELETED (search key) .......................................   39
     DRAFT (search key) .........................................   39
     ENVELOPE (fetch item) ......................................   44
     ENVELOPE (fetch result) ....................................   62
     EXAMINE (command) ..........................................   24
     EXISTS (response) ..........................................   56
     EXPUNGE (command) ..........................................   37
     EXPUNGE (response) .........................................   57
     Envelope Structure (message attribute) .....................   11
     FAST (fetch item) ..........................................   44
     FETCH (command) ............................................   41
     FETCH (response) ...........................................   58
     FLAGGED (search key) .......................................   39
     FLAGS (fetch item) .........................................   44
     FLAGS (fetch result) .......................................   62
     FLAGS (response) ...........................................   56
     FLAGS <flag list> (store command data item) ................   45
     FLAGS.SILENT <flag list> (store command data item) .........   45
     FROM <string> (search key) .................................   39
     FULL (fetch item) ..........................................   44
     Flags (message attribute) ..................................    9
     HEADER (part specifier) ....................................   41
     HEADER <field-name> <string> (search key) ..................   39
     HEADER.FIELDS <header_list> (part specifier) ...............   41
     HEADER.FIELDS.NOT <header_list> (part specifier) ...........   41
     INTERNALDATE (fetch item) ..................................   44
     INTERNALDATE (fetch result) ................................   62
     Internal Date (message attribute) ..........................   10
     KEYWORD <flag> (search key) ................................   39
     Keyword (type of flag) .....................................   10

Crispin Standards Track [Page 80] RFC 2060 IMAP4rev1 December 1996

     LARGER <n> (search key) ....................................   39
     LIST (command) .............................................   30
     LIST (response) ............................................   54
     LOGIN (command) ............................................   22
     LOGOUT (command) ...........................................   20
     LSUB (command) .............................................   32
     LSUB (response) ............................................   55
     MAY (specification requirement term) .......................    5
     MESSAGES (status item) .....................................   33
     MIME (part specifier) ......................................   42
     MUST (specification requirement term) ......................    4
     MUST NOT (specification requirement term) ..................    4
     Message Sequence Number (message attribute) ................    9
     NEW (search key) ...........................................   39
     NEWNAME (response code) ....................................   50
     NO (response) ..............................................   51
     NOOP (command) .............................................   19
     NOT <search-key> (search key) ..............................   39
     OK (response) ..............................................   51
     OLD (search key) ...........................................   39
     ON <date> (search key) .....................................   39
     OPTIONAL (specification requirement term) ..................    5
     OR <search-key1> <search-key2> (search key) ................   39
     PARSE (response code) ......................................   50
     PERMANENTFLAGS (response code) .............................   50
     PREAUTH (response) .........................................   52
     Permanent Flag (class of flag) .............................   10
     READ-ONLY (response code) ..................................   50
     READ-WRITE (response code) .................................   50
     RECENT (response) ..........................................   57
     RECENT (search key) ........................................   39
     RECENT (status item) .......................................   33
     RENAME (command) ...........................................   27
     REQUIRED (specification requirement term) ..................    4
     RFC822 (fetch item) ........................................   44
     RFC822 (fetch result) ......................................   63
     RFC822.HEADER (fetch item) .................................   44
     RFC822.HEADER (fetch result) ...............................   62
     RFC822.SIZE (fetch item) ...................................   44
     RFC822.SIZE (fetch result) .................................   62
     RFC822.TEXT (fetch item) ...................................   44
     RFC822.TEXT (fetch result) .................................   62
     SEARCH (command) ...........................................   37
     SEARCH (response) ..........................................   55
     SEEN (search key) ..........................................   40
     SELECT (command) ...........................................   23
     SENTBEFORE <date> (search key) .............................   40
     SENTON <date> (search key) .................................   40

Crispin Standards Track [Page 81] RFC 2060 IMAP4rev1 December 1996

     SENTSINCE <date> (search key) ..............................   40
     SHOULD (specification requirement term) ....................    5
     SHOULD NOT (specification requirement term) ................    5
     SINCE <date> (search key) ..................................   40
     SMALLER <n> (search key) ...................................   40
     STATUS (command) ...........................................   33
     STATUS (response) ..........................................   55
     STORE (command) ............................................   45
     SUBJECT <string> (search key) ..............................   40
     SUBSCRIBE (command) ........................................   29
     Session Flag (class of flag) ...............................   10
     System Flag (type of flag) .................................    9
     TEXT (part specifier) ......................................   42
     TEXT <string> (search key) .................................   40
     TO <string> (search key) ...................................   40
     TRYCREATE (response code) ..................................   51
     UID (command) ..............................................   47
     UID (fetch item) ...........................................   44
     UID (fetch result) .........................................   63
     UID <message set> (search key) .............................   40
     UIDNEXT (status item) ......................................   33
     UIDVALIDITY (response code) ................................   51
     UIDVALIDITY (status item) ..................................   34
     UNANSWERED (search key) ....................................   40
     UNDELETED (search key) .....................................   40
     UNDRAFT (search key) .......................................   40
     UNFLAGGED (search key) .....................................   40
     UNKEYWORD <flag> (search key) ..............................   40
     UNSEEN (response code) .....................................   51
     UNSEEN (search key) ........................................   40
     UNSEEN (status item) .......................................   34
     UNSUBSCRIBE (command) ......................................   30
     Unique Identifier (UID) (message attribute) ................    7
     X<atom> (command) ..........................................   48
     [RFC-822] Size (message attribute) .........................   11
     \Answered (system flag) ....................................    9
     \Deleted (system flag) .....................................    9
     \Draft (system flag) .......................................    9
     \Flagged (system flag) .....................................    9
     \Marked (mailbox name attribute) ...........................   54
     \Noinferiors (mailbox name attribute) ......................   54
     \Noselect (mailbox name attribute) .........................   54
     \Recent (system flag) ......................................   10
     \Seen (system flag) ........................................    9
     \Unmarked (mailbox name attribute) .........................   54

Crispin Standards Track [Page 82]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2060.txt · Last modified: 1996/12/02 21:16 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki