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rfc:rfc4409

Network Working Group R. Gellens Request for Comments: 4409 QUALCOMM Obsoletes: 2476 J. Klensin Category: Standards Track April 2006

                     Message Submission for Mail

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.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 This memo splits message submission from message relay, allowing each
 service to operate according to its own rules (for security, policy,
 etc.), and specifies what actions are to be taken by a submission
 server.
 Message relay and final delivery are unaffected, and continue to use
 SMTP over port 25.
 When conforming to this document, message submission uses the
 protocol specified here, normally over port 587.
 This separation of function offers a number of benefits, including
 the ability to apply specific security or policy requirements.

Gellens & Klensin Standards Track [Page 1] RFC 4409 Message Submission for Mail April 2006

Table of Contents

 1. Introduction ....................................................3
 2. Document Information ............................................4
    2.1. Definitions of Terms Used in This Memo .....................4
    2.2. Conventions Used in This Document ..........................5
 3. Message Submission ..............................................5
    3.1. Submission Identification ..................................5
    3.2. Message Rejection and Bouncing .............................5
    3.3. Authorized Submission ......................................6
 4. Mandatory Actions ...............................................7
    4.1. General Submission Rejection Code ..........................7
    4.2. Ensure All Domains Are Fully-Qualified .....................7
    4.3. Require Authentication .....................................8
 5. Recommended Actions .............................................8
    5.1. Enforce Address Syntax .....................................8
    5.2. Log Errors .................................................8
 6. Optional Actions ................................................9
    6.1. Enforce Submission Rights ..................................9
    6.2. Enforce Permissions ........................................9
    6.3. Check Message Data .........................................9
    6.4. Support for the Postmaster Address .........................9
 7. Interaction with SMTP Extensions ...............................10
 8. Message Modifications ..........................................11
    8.1. Add 'Sender' ..............................................11
    8.2. Add 'Date' ................................................11
    8.3. Add 'Message-ID' ..........................................11
    8.4. Transfer Encode ...........................................11
    8.5. Sign the Message ..........................................11
    8.6. Encrypt the Message .......................................12
    8.7. Resolve Aliases ...........................................12
    8.8. Header Rewriting ..........................................12
 9. Security Considerations ........................................12
 10. IANA Considerations ...........................................13
 11. Acknowledgements ..............................................13
 12. Normative References ..........................................14
 13. Informative References ........................................14

Gellens & Klensin Standards Track [Page 2] RFC 4409 Message Submission for Mail April 2006

1. Introduction

 SMTP was defined as a message *transfer* protocol, that is, a means
 to route (if needed) and deliver finished (complete) messages.
 Message Transfer Agents (MTAs) are not supposed to alter the message
 text, except to add 'Received', 'Return-Path', and other header
 fields as required by [SMTP-MTA].
 However, SMTP is now also widely used as a message *submission*
 protocol, that is, a means for Message User Agents (MUAs) to
 introduce new messages into the MTA routing network.  The process
 that accepts message submissions from MUAs is termed a Message
 Submission Agent (MSA).
 In order to permit unconstrained communications, SMTP is not often
 authenticated during message relay.
 Authentication and authorization of initial submissions have become
 increasingly important, driven by changes in security requirements
 and rising expectations that submission servers take responsibility
 for the message traffic they originate.
 For example, due to the prevalence of machines that have worms,
 viruses, or other malicious software that generate large amounts of
 spam, many sites now prohibit outbound traffic on the standard SMTP
 port (port 25), funneling all mail submissions through submission
 servers.
 In addition to authentication and authorization issues, messages
 being submitted are in some cases finished (complete) messages, and
 in other cases are unfinished (incomplete) in one or more aspects.
 Unfinished messages may need to be completed to ensure they conform
 to [MESSAGE-FORMAT], and later requirements.  For example, the
 message may lack a proper 'Date' header field, and domains might not
 be fully qualified.  In some cases, the MUA may be unable to generate
 finished messages (e.g., it might not know its time zone).  Even when
 submitted messages are complete, local site policy may dictate that
 the message text be examined or modified in some way, e.g., to
 conceal local name or address spaces.  Such completions or
 modifications have been shown to cause harm when performed by
 downstream MTAs -- that is, MTAs after the first-hop submission MTA
 -- and are in general considered to be outside the province of
 standardized MTA functionality.
 Separating messages into submissions and transfers allows developers
 and network administrators to more easily do the following:

Gellens & Klensin Standards Track [Page 3] RFC 4409 Message Submission for Mail April 2006

  • Implement security policies and guard against unauthorized mail

relaying or injection of unsolicited bulk mail

  • Implement authenticated submission, including off-site submission

by authorized users such as travelers

  • Separate the relevant software code differences, thereby making

each code base more straightforward and allowing for different

     programs for relay and submission
  • Detect configuration problems with a site's mail clients
  • Provide a basis for adding enhanced submission services in the

future

 This memo describes a low-cost, deterministic means for messages to
 be identified as submissions, and specifies what actions are to be
 taken by a submission server.

2. Document Information

2.1. Definitions of Terms Used in This Memo

 Many of the concepts and terms used in this document are defined in
 [SMTP-MTA]; familiarity with those documents is assumed here.
 Fully-Qualified
 Containing or consisting of a domain that can be globally resolved
 using the Domain Name Service; that is, not a local alias or partial
 specification.
 Message Submission Agent (MSA)
 A process that conforms to this specification.  An MSA acts as a
 submission server to accept messages from MUAs, and either delivers
 them or acts as an SMTP client to relay them to an MTA.
 Message Transfer Agent (MTA)
 A process that conforms to [SMTP-MTA].  An MTA acts as an SMTP server
 to accept messages from an MSA or another MTA, and either delivers
 them or acts as an SMTP client to relay them to another MTA.

Gellens & Klensin Standards Track [Page 4] RFC 4409 Message Submission for Mail April 2006

 Message User Agent (MUA)
 A process that acts (often on behalf of a user and with a user
 interface) to compose and submit new messages, and process delivered
 messages.
 For delivered messages, the receiving MUA may obtain and process the
 message according to local conventions or, in what is commonly
 referred to as a split-MUA model, Post Office Protocol [POP3] or IMAP
 [IMAP4] is used to access delivered messages, whereas the protocol
 defined here (or SMTP) is used to submit messages.

2.2. Conventions Used in This Document

 In examples, "C:" is used to indicate lines sent by the client, and
 "S:" indicates those sent by the server.  Line breaks within a
 command example are for editorial purposes only.
 Examples use the 'example.net' domain.
 The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
 in this document are to be interpreted as defined in [KEYWORDS].

3. Message Submission

3.1. Submission Identification

 Port 587 is reserved for email message submission as specified in
 this document.  Messages received on this port are defined to be
 submissions.  The protocol used is ESMTP [SMTP-MTA, ESMTP], with
 additional restrictions or allowances as specified here.
 Although most email clients and servers can be configured to use port
 587 instead of 25, there are cases where this is not possible or
 convenient.  A site MAY choose to use port 25 for message submission,
 by designating some hosts to be MSAs and others to be MTAs.

3.2. Message Rejection and Bouncing

 MTAs and MSAs MAY implement message rejection rules that rely in part
 on whether the message is a submission or a relay.
 For example, some sites might configure their MTAs to reject all RCPT
 commands for messages that do not reference local users, and
 configure their MSA to reject all message submissions that do not
 come from authorized users, with authorization based either on
 authenticated identity or the submitting endpoint being within a
 protected IP environment.

Gellens & Klensin Standards Track [Page 5] RFC 4409 Message Submission for Mail April 2006

 NOTE:  It is better to reject a message than to risk sending one that
 is damaged.  This is especially true for problems that are
 correctable by the MUA, for example, an invalid 'From' field.
 If an MSA is not able to determine a return path to the submitting
 user, from a valid MAIL FROM, a valid source IP address, or based on
 authenticated identity, then the MSA SHOULD immediately reject the
 message.  A message can be immediately rejected by returning a 550
 code to the MAIL command.
 Note that a null return path, that is, MAIL FROM:<>, is permitted and
 MUST NOT in itself be cause for rejecting a message.  (MUAs need to
 generate null return-path messages for a variety of reasons,
 including disposition notifications.)
 Except in the case where the MSA is unable to determine a valid
 return path for the message being submitted, text in this
 specification that instructs an MSA to issue a rejection code MAY be
 complied with by accepting the message and subsequently generating a
 bounce message.  (That is, if the MSA is going to reject a message
 for any reason except being unable to determine a return path, it can
 optionally do an immediate rejection or accept the message and then
 mail a bounce.)
 NOTE:  In the normal case of message submission, immediately
 rejecting the message is preferred, as it gives the user and MUA
 direct feedback.  To properly handle delayed bounces, the client MUA
 needs to maintain a queue of messages it has submitted, and match
 bounces to them.  Note that many contemporary MUAs do not have this
 capability.

3.3. Authorized Submission

 Numerous methods have been used to ensure that only authorized users
 are able to submit messages.  These methods include authenticated
 SMTP, IP address restrictions, secure IP and other tunnels, and prior
 POP authentication.
 Authenticated SMTP [SMTP-AUTH] has seen widespread deployment.  It
 allows the MSA to determine an authorization identity for the message
 submission, one that is not tied to other protocols.
 IP address restrictions are very widely implemented, but do not allow
 for travelers and similar situations, and can be easily spoofed
 unless all transport paths between the MUA and MSA are trustworthy.

Gellens & Klensin Standards Track [Page 6] RFC 4409 Message Submission for Mail April 2006

 Secure IP [IPSEC], and other encrypted and authenticated tunneling
 techniques, can also be used and provide additional benefits of
 protection against eavesdropping and traffic analysis.
 Requiring a POP [POP3] authentication (from the same IP address)
 within some amount of time (e.g., 20 minutes) prior to the start of a
 message submission session has also been used, but this does impose
 restrictions on clients as well as servers, which may cause
 difficulties.  Specifically, the client must do a POP authentication
 before an SMTP submission session, and not all clients are capable
 and configured for this.  Also, the MSA must coordinate with the POP
 server, which may be difficult.  There is also a window during which
 an unauthorized user can submit messages and appear to be a
 previously authorized user.  Since it is dependent on the MUA's IP
 addresses, this technique is substantially as subject to IP address
 spoofing as validation based on known IP addresses alone (see above).

4. Mandatory Actions

 An MSA MUST do all of the following:

4.1. General Submission Rejection Code

 Unless covered by a more precise response code, response code 554 is
 to be used to reject a MAIL, RCPT, or DATA command that contains
 something improper.

4.2. Ensure All Domains Are Fully-Qualified

 The MSA MUST ensure that all domains in the SMTP envelope are fully-
 qualified.
 If the MSA examines or alters the message text in any way, except to
 add trace header fields [SMTP-MTA], it MUST ensure that all domains
 in address header fields are fully-qualified.
 Reply code 554 is to be used to reject a MAIL, RCPT, or DATA command
 that contains improper domain references.
 A frequent local convention is to accept single-level domains (e.g.,
 'sales') and then to expand the reference by adding the remaining
 portion of the domain name (e.g., to 'sales.example.net').  Local
 conventions that permit single-level domains SHOULD reject, rather
 than expand, incomplete multi-level domains (e.g., 'squeaky.sales'),
 since such expansion is particularly risky.

Gellens & Klensin Standards Track [Page 7] RFC 4409 Message Submission for Mail April 2006

4.3. Require Authentication

 The MSA MUST by default issue an error response to the MAIL command
 if the session has not been authenticated using [SMTP-AUTH], unless
 it has already independently established authentication or
 authorization (such as being within a protected subnetwork).
 Section 3.3 discusses authentication mechanisms.
 Reply code 530 [SMTP-AUTH] is used for this purpose.

5. Recommended Actions

 The MSA SHOULD do all of the following:

5.1. Enforce Address Syntax

 An MSA SHOULD reject messages with illegal syntax in a sender or
 recipient SMTP envelope address.
 If the MSA examines or alters the message text in way, except to add
 trace header fields, it SHOULD reject messages with illegal address
 syntax in address header fields.
 Reply code 501 is to be used to reject a MAIL or RCPT command that
 contains a detectably improper address.
 When addresses are resolved after submission of the message body,
 reply code 554 (with a suitable enhanced status code from
 [SMTP-CODES]) is used after end-of-data, if the message contains
 invalid addresses in the header.

5.2. Log Errors

 The MSA SHOULD log message errors, especially apparent
 misconfigurations of client software.
 It can be very helpful to notify the administrator when problems are
 detected with local mail clients.  This is another advantage of
 distinguishing submission from relay: system administrators might be
 interested in local configuration problems, but not in client
 problems at other sites.
 Note that it is important to impose limits on such logging to prevent
 certain forms of denial of service (DoS) attacks.

Gellens & Klensin Standards Track [Page 8] RFC 4409 Message Submission for Mail April 2006

6. Optional Actions

 The MSA MAY do any of the following:

6.1. Enforce Submission Rights

 The MSA MAY issue an error response to a MAIL command if the address
 in MAIL FROM appears to have insufficient submission rights, or is
 not authorized with the authentication used (if the session has been
 authenticated).
 Reply code 550 with an appropriate enhanced status code per
 [SMTP-CODES], such as 5.7.1, is used for this purpose.

6.2. Enforce Permissions

 The MSA MAY issue an error response to a RCPT command if inconsistent
 with the permissions given to the user (if the session has been
 authenticated).
 Reply code 550 with an appropriate enhanced status code per
 [SMTP-CODES], such as 5.7.1, is used for this purpose.

6.3. Check Message Data

 The MSA MAY issue an error response to the DATA command or send a
 failure result after end-of-data if the submitted message is
 syntactically invalid, or seems inconsistent with permissions given
 to the user (if known), or violates site policy in some way.
 Reply code 554 is used for syntactic problems in the data.  Reply
 code 501 is used if the command itself is not syntactically valid.
 Reply code 550 with an appropriate enhanced status code per
 [SMTP-CODES] (such as 5.7.1) is used to reject based on the
 submitting user.  Reply code 550 with an appropriate enhanced status
 code (such as 5.7.0) is used if the message violates site policy.

6.4. Support for the Postmaster Address

 If appropriate under local conditions and to facilitate conformance
 with the "postmaster" requirements of [SMTP-MTA], the MSA MAY permit
 a reduced degree of authentication for mail addressed to the
 "postmaster" (or one of its alternate spelling forms, see
 [SMTP-MTA]), in one or more domains, as compared to requirements
 enforced for other addresses.  Among other benefits, this provides an
 address of last resort that can be used by authorized users to report
 problems that otherwise prevent them from submitting mail.

Gellens & Klensin Standards Track [Page 9] RFC 4409 Message Submission for Mail April 2006

7. Interaction with SMTP Extensions

 The following table lists the current standards-track and
 Experimental SMTP extensions.  Listed are the EHLO keyword, name, an
 indication as to the use of the extension on the submit port, and a
 reference:

Keyword Name Submission Reference ———- ————————– ———- —————- PIPELINING Pipelining SHOULD [PIPELINING] ENHANCEDSTATUSCODES Enhanced Status Codes SHOULD [CODES-EXTENSION] ETRN Extended Turn MUST NOT [ETRN] … Extended Codes SHOULD [SMTP-CODES] DSN Delivery Status Notification SHOULD [DSN] SIZE Message size MAY [SIZE] … 521 reply code MUST NOT [521REPLY] CHECKPOINT Checkpoint/Restart MAY [CHECKPOINT] BINARYMIME Binary MIME MAY [CHUNKING] CHUNKING Chunking MAY [CHUNKING] 8BITMIME Use 8-bit data SHOULD [8BITMIME] AUTH Authentication MUST [SMTP-AUTH] STARTTLS Start TLS MAY [Start-TLS] NO-SOLICITING Notification of no soliciting MAY [Msg-Track] MTRK Message Tracking MAY [Msg-Track]

 Future SMTP extensions SHOULD explicitly specify if they are valid on
 the Submission port.
 Some SMTP extensions are especially useful for message submission:
 Extended Status Codes [SMTP-CODES] SHOULD be supported and used
 according to [CODES-EXTENSION].  This permits the MSA to notify the
 client of specific configuration or other problems in more detail
 than the response codes listed in this memo.  Because some rejections
 are related to a site's security policy, care should be used not to
 expose more detail to unauthenticated senders than is needed
 [PIPELINING] SHOULD be supported by the MSA.
 [SMTP-AUTH] allows the MSA to validate the authority and determine
 the identity of the submitting user and MUST be supported by the MSA.
 Any references to the DATA command in this memo also refer to any
 substitutes for DATA, such as the BDAT command used with [CHUNKING].

Gellens & Klensin Standards Track [Page 10] RFC 4409 Message Submission for Mail April 2006

8. Message Modifications

 Sites MAY modify submissions to ensure compliance with standards and
 site policy.  This section describes a number of such modifications
 that are often considered useful.
 NOTE:  As a matter of guidance for local decisions to implement
 message modification, a paramount rule is to limit such actions to
 remedies for specific problems that have clear solutions.  This is
 especially true with address elements.  For example, indiscriminately
 appending a domain to an address or element that lacks one typically
 results in more broken addresses.  An unqualified address must be
 verified to be a valid local part in the domain before the domain can
 be safely added.
 Any message forwarded or delivered by the MSA MUST conform to the
 requirements of [SMTP-MTA] and [MESSAGE-FORMAT].

8.1. Add 'Sender'

 The MSA MAY add or replace the 'Sender' field, if the identity of the
 sender is known and this is not given in the 'From' field.
 The MSA MUST ensure that any address it places in a 'Sender' field is
 in fact a valid mail address.

8.2. Add 'Date'

 The MSA MAY add a 'Date' field to the submitted message, if it lacks
 it, or correct the 'Date' field if it does not conform to
 [MESSAGE-FORMAT] syntax.

8.3. Add 'Message-ID'

 The MSA SHOULD add or replace the 'Message-ID' field, if it lacks it,
 or it is not valid syntax (as defined by [MESSAGE-FORMAT]).  Note
 that a number of clients still do not generate Message-ID fields.

8.4. Transfer Encode

 The MSA MAY apply transfer encoding to the message according to MIME
 conventions, if needed and not harmful to the MIME type.

8.5. Sign the Message

 The MSA MAY (digitally) sign or otherwise add authentication
 information to the message.

Gellens & Klensin Standards Track [Page 11] RFC 4409 Message Submission for Mail April 2006

8.6. Encrypt the Message

 The MSA MAY encrypt the message for transport to reflect
 organizational policies.
 NOTE:  To be useful, the addition of a signature and/or encryption by
 the MSA generally implies that the connection between the MUA and MSA
 must itself be secured in some other way, for example, by operating
 inside of a secure environment, by securing the submission connection
 at the transport layer, or by using an [SMTP-AUTH] mechanism that
 provides for session integrity.

8.7. Resolve Aliases

 The MSA MAY resolve aliases (CNAME records) for domain names, in the
 SMTP envelope and optionally in address fields of the header, subject
 to local policy.
 NOTE:  Unconditionally resolving aliases could be harmful.  For
 example, if www.example.net and ftp.example.net are both aliases for
 mail.example.net, rewriting them could lose useful information.

8.8. Header Rewriting

 The MSA MAY rewrite local parts and/or domains in the SMTP envelope,
 and optionally in address fields of the header, according to local
 policy.  For example, a site may prefer to rewrite 'JRU' as
 'J.Random.User' in order to hide login names, and/or to rewrite
 'squeaky.sales.example.net' as 'zyx.example.net' to hide machine
 names and make it easier to move users.
 However, only addresses, local-parts, or domains which match specific
 local MSA configuration settings should be altered.  It would be very
 dangerous for the MSA to apply data-independent rewriting rules, such
 as always deleting the first element of a domain name.  So, for
 example, a rule that strips the left-most element of the domain, if
 the complete domain matches '*.foo.example.net', would be acceptable.
 The MSA MUST NOT rewrite a forward-pointing (destination) address in
 a way that violates the constraints of [SMTP-MTA] on modifications of
 local-parts.

9. Security Considerations

 Separation of submission and relay of messages allows a site to
 implement different policies for the two types of services, including
 requiring use of additional security mechanisms for one or both.  It
 can do this in a way which is simpler, both technically and

Gellens & Klensin Standards Track [Page 12] RFC 4409 Message Submission for Mail April 2006

 administratively.  This increases the likelihood that policies will
 be applied correctly.
 Separation also can aid in tracking and preventing unsolicited bulk
 email.
 For example, a site could configure its mail servers such that the
 MSA requires authentication before accepting a message, and the MTA
 rejects all RCPT commands for non-local users.  This can be an
 important element in a site's total email security policy.
 If a site fails to require any form of authorization for message
 submissions (see section 3.3 for discussion), it is allowing open use
 of its resources and name; unsolicited bulk email can be injected
 using its facilities.
 Section 3 includes further discussion of issues with some
 authentication methods.
 Section 5.2 includes a cautionary note that unlimited logging can
 enable certain forms of denial of service attacks.

10. IANA Considerations

 The registration for port 587 has been updated to refer to this memo
 rather than RFC 2476.

11. Acknowledgements

 Nathaniel Borenstein and Barry Leiba were instrumental in the
 development of this update to RFC 2476.
 The original memo (RFC 2476) was developed in part based on comments
 and discussions which took place on and off the IETF-Submit mailing
 list.  The help of those who took the time to review that document
 and make suggestions is appreciated, especially that of Dave Crocker,
 Ned Freed, Keith Moore, John Myers, and Chris Newman.
 Special thanks to Harald Alvestrand, who got this effort started.

Gellens & Klensin Standards Track [Page 13] RFC 4409 Message Submission for Mail April 2006

12. Normative References

 [ESMTP]           Klensin, J., Freed, N., Rose, M., Stefferud, E.,
                   and D. Crocker, "SMTP Service Extensions", STD 10,
                   RFC 1869, November 1995.
 [KEYWORDS]        Bradner, S., "Key words for use in RFCs to Indicate
                   Requirement Levels", BCP 14, RFC 2119, March 1997.
 [SMTP-MTA]        Postel, J., "Simple Mail Transfer Protocol", STD
                   10, RFC 821, August 1982.
                   Partridge, C., "Mail routing and the domain
                   system", STD 10, RFC 974, January 1986.
                   Braden, R., "Requirements for Internet Hosts -
                   Application and Support", STD 3, RFC 1123, October
                   1989.
                   Klensin, J., "Simple Mail Transfer Protocol", RFC
                   2821, April 2001.

13. Informative References

 [521REPLY]        Durand, A. and F. Dupont, "SMTP 521 Reply Code",
                   RFC 1846, September 1995.
 [8BITMIME]        Klensin, J., Freed, N., Rose, M., Stefferud, E.,
                   and D. Crocker, "SMTP Service Extension for 8bit-
                   MIMEtransport", RFC 1652, July 1994.
 [CHECKPOINT]      Crocker, D., Freed, N., and A. Cargille, "SMTP
                   Service Extension for Checkpoint/Restart", RFC
                   1845, September 1995.
 [CHUNKING]        Vaudreuil, G., "SMTP Service Extensions for
                   Transmission of Large and Binary MIME Messages",
                   RFC 3030, December 2000.
 [CODES-EXTENSION] Freed, N., "SMTP Service Extension for Returning
                   Enhanced Error Codes", RFC 2034, October 1996.
 [DSN]             Moore, K., "Simple Mail Transfer Protocol (SMTP)
                   Service Extension for Delivery Status Notifications
                   (DSNs)", RFC 3461, January 2003.
 [ETRN]            De Winter, J., "SMTP Service Extension for Remote
                   Message Queue Starting", RFC 1985, August 1996.

Gellens & Klensin Standards Track [Page 14] RFC 4409 Message Submission for Mail April 2006

 [IMAP4]           Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
                   VERSION 4rev1", RFC 3501, March 2003.
 [IPSEC]           Kent, S. and R. Atkinson, "Security Architecture
                   for the Internet Protocol", RFC 2401, November
                   1998.
 [MESSAGE-FORMAT]  Crocker, D., "Standard for the format of ARPA
                   Internet text messages", STD 11, RFC 822, August
                   1982.
                   Braden, R., "Requirements for Internet Hosts -
                   Application and Support", STD 3, RFC 1123, October
                   1989.
                   Resnick, P., "Internet Message Format", RFC 2822,
                   April 2001.
 [Msg-Track]       Allman, E. and T. Hansen, "SMTP Service Extension
                   for Message Tracking", RFC 3885, September 2004.
 [PIPELINING]      Freed, N., "SMTP Service Extension for Command
                   Pipelining", STD 60, RFC 2920, September 2000.
 [POP3]            Myers, J. and M. Rose, "Post Office Protocol -
                   Version 3", STD 53, RFC 1939, May 1996.
 [SIZE]            Klensin, J., Freed, N., and K. Moore, "SMTP Service
                   Extension for Message Size Declaration", STD 10,
                   RFC 1870, November 1995.
 [SMTP-AUTH]       Myers, J., "SMTP Service Extension for
                   Authentication", RFC 2554, March 1999.
 [SMTP-CODES]      Vaudreuil, G., "Enhanced Mail System Status Codes",
                   RFC 3463, January 2003.
 [Start-TLS]       Hoffman, P., "SMTP Service Extension for Secure
                   SMTP over Transport Layer Security", RFC 3207,
                   February 2002.

Gellens & Klensin Standards Track [Page 15] RFC 4409 Message Submission for Mail April 2006

Authors' Addresses

 Randall Gellens
 QUALCOMM Incorporated
 5775 Morehouse Drive
 San Diego, CA  92121-2779
 USA
 EMail: rg+ietf@qualcomm.com
 John C. Klensin
 1770 Massachusetts Ave, #322
 Cambridge, MA 02140
 USA
 EMail: john+ietf@jck.com

Gellens & Klensin Standards Track [Page 16] RFC 4409 Message Submission for Mail April 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
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 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
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 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
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 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Gellens & Klensin Standards Track [Page 17]

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