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rfc:rfc3463

Network Working Group G. Vaudreuil Request for Comments: 3463 Lucent Technologies Obsoletes: 1893 January 2003 Category: Standards Track

                 Enhanced Mail System Status Codes

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 (2003).  All Rights Reserved.

Abstract

 This document defines a set of extended status codes for use within
 the mail system for delivery status reports, tracking, and improved
 diagnostics.  In combination with other information provided in the
 Delivery Status Notification (DSN) delivery report, these codes
 facilitate media and language independent rendering of message
 delivery status.

Table of Contents

 1.   Overview ......................................................2
 2.   Status Code Structure .........................................3
 3.   Enumerated Status Codes .......................................5
   3.1  Other or Undefined Status ...................................6
   3.2  Address Status ..............................................6
   3.3  Mailbox Status ..............................................7
   3.4  Mail system status ..........................................8
   3.5  Network and Routing Status ..................................9
   3.6  Mail Delivery Protocol Status ..............................10
   3.7  Message Content or Message Media Status ....................11
   3.8  Security or Policy Status ..................................12
 4.   References ...................................................13
 5.   Security Considerations ......................................13
      Appendix A - Collected Status Codes ..........................14
      Appendix B - Changes from RFC1893 ............................15
      Author's Address .............................................15
      Full Copyright Statement .....................................16

Vaudreuil Standards Track [Page 1] RFC 3463 Enhanced Mail System Status Codes January 2003

1. Overview

 There is a need for a standard mechanism for the reporting of mail
 system errors richer than the limited set offered by SMTP and the
 system specific text descriptions sent in mail messages.  There is a
 pressing need for a rich machine-readable, human language independent
 status code for use in delivery status notifications [DSN].  This
 document proposes a new set of status codes for this purpose.
 SMTP [SMTP] error codes have historically been used for reporting
 mail system errors.  Because of limitations in the SMTP code design,
 these are not suitable for use in delivery status notifications.
 SMTP provides about 12 useful codes for delivery reports.  The
 majority of the codes are protocol specific response codes such as
 the 354 response to the SMTP data command.  Each of the 12 useful
 codes are overloaded to indicate several error conditions.  SMTP
 suffers some scars from history, most notably the unfortunate damage
 to the reply code extension mechanism by uncontrolled use.  This
 proposal facilitates future extensibility by requiring the client to
 interpret unknown error codes according to the theory of codes while
 requiring servers to register new response codes.
 The SMTP theory of reply codes are partitioned in the number space in
 such a manner that the remaining available codes will not provide the
 space needed.  The most critical example is the existence of only 5
 remaining codes for mail system errors.  The mail system
 classification includes both host and mailbox error conditions.  The
 remaining third digit space would be completely consumed as needed to
 indicate MIME and media conversion errors and security system errors.
 A revision to the SMTP theory of reply codes to better distribute the
 error conditions in the number space will necessarily be incompatible
 with SMTP.  Further, consumption of the remaining reply-code number
 space for delivery notification reporting will reduce the available
 codes for new ESMTP extensions.
 The following status code set is based on the SMTP theory of reply
 codes.  It adopts the success, permanent error, and transient error
 semantics of the first value, with a further description and
 classification in the second.  This proposal re-distributes the
 classifications to better distribute the error conditions, such as
 separating mailbox from host errors.
 Document Conventions
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14 [RFC2119].

Vaudreuil Standards Track [Page 2] RFC 3463 Enhanced Mail System Status Codes January 2003

2. Status Code Structure

 This document defines a new set of status codes to report mail system
 conditions.  These status codes are used for media and language
 independent status reporting.  They are not intended for system
 specific diagnostics.
 The syntax of the new status codes is defined as:
    status-code = class "." subject "." detail
    class = "2"/"4"/"5"
    subject = 1*3digit
    detail = 1*3digit
 White-space characters and comments are NOT allowed within a status-
 code.  Each numeric sub-code within the status-code MUST be expressed
 without leading zero digits.
 Status codes consist of three numerical fields separated by ".".  The
 first sub-code indicates whether the delivery attempt was successful.
 The second sub-code indicates the probable source of any delivery
 anomalies, and the third sub-code indicates a precise error
 condition.
 Example:  2.1.23
 The code space defined is intended to be extensible only by standards
 track documents.  Mail system specific status codes should be mapped
 as close as possible to the standard status codes.  Servers should
 send only defined, registered status codes.  System specific errors
 and diagnostics should be carried by means other than status codes.
 New subject and detail codes will be added over time.  Because the
 number space is large, it is not intended that published status codes
 will ever be redefined or eliminated.  Clients should preserve the
 extensibility of the code space by reporting the general error
 described in the subject sub-code when the specific detail is
 unrecognized.

Vaudreuil Standards Track [Page 3] RFC 3463 Enhanced Mail System Status Codes January 2003

 The class sub-code provides a broad classification of the status.
 The enumerated values for each class are defined as:
    2.XXX.XXX   Success
       Success specifies that the DSN is reporting a positive delivery
       action.  Detail sub-codes may provide notification of
       transformations required for delivery.
    4.XXX.XXX   Persistent Transient Failure
       A persistent transient failure is one in which the message as
       sent is valid, but persistence of some temporary condition has
       caused abandonment or delay of attempts to send the message.
       If this code accompanies a delivery failure report, sending in
       the future may be successful.
    5.XXX.XXX   Permanent Failure
       A permanent failure is one which is not likely to be resolved
       by resending the message in the current form.  Some change to
       the message or the destination must be made for successful
       delivery.
 A client must recognize and report class sub-code even where
 subsequent subject sub-codes are unrecognized.
 The subject sub-code classifies the status.  This value applies to
 each of the three classifications.  The subject sub-code, if
 recognized, must be reported even if the additional detail provided
 by the detail sub-code is not recognized.  The enumerated values for
 the subject sub-code are:
    X.0.XXX   Other or Undefined Status
       There is no additional subject information available.
    X.1.XXX Addressing Status
       The address status reports on the originator or destination
       address.  It may include address syntax or validity.  These
       errors can generally be corrected by the sender and retried.
    X.2.XXX Mailbox Status
       Mailbox status indicates that something having to do with the
       mailbox has caused this DSN.  Mailbox issues are assumed to be
       under the general control of the recipient.

Vaudreuil Standards Track [Page 4] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.3.XXX Mail System Status
       Mail system status indicates that something having to do with
       the destination system has caused this DSN.  System issues are
       assumed to be under the general control of the destination
       system administrator.
    X.4.XXX Network and Routing Status
       The networking or routing codes report status about the
       delivery system itself.  These system components include any
       necessary infrastructure such as directory and routing
       services.  Network issues are assumed to be under the control
       of the destination or intermediate system administrator.
    X.5.XXX Mail Delivery Protocol Status
       The mail delivery protocol status codes report failures
       involving the message delivery protocol.  These failures
       include the full range of problems resulting from
       implementation errors or an unreliable connection.
    X.6.XXX Message Content or Media Status
       The message content or media status codes report failures
       involving the content of the message.  These codes report
       failures due to translation, transcoding, or otherwise
       unsupported message media.  Message content or media issues are
       under the control of both the sender and the receiver, both of
       which must support a common set of supported content-types.
    X.7.XXX Security or Policy Status
       The security or policy status codes report failures involving
       policies such as per-recipient or per-host filtering and
       cryptographic operations.  Security and policy status issues
       are assumed to be under the control of either or both the
       sender and recipient.  Both the sender and recipient must
       permit the exchange of messages and arrange the exchange of
       necessary keys and certificates for cryptographic operations.

3. Enumerated Status Codes

 The following section defines and describes the detail sub-code.  The
 detail value provides more information about the status and is
 defined relative to the subject of the status.

Vaudreuil Standards Track [Page 5] RFC 3463 Enhanced Mail System Status Codes January 2003

3.1 Other or Undefined Status

    X.0.0   Other undefined Status
       Other undefined status is the only undefined error code.  It
       should be used for all errors for which only the class of the
       error is known.

3.2 Address Status

    X.1.0   Other address status
       Something about the address specified in the message caused
       this DSN.
    X.1.1   Bad destination mailbox address
       The mailbox specified in the address does not exist.  For
       Internet mail names, this means the address portion to the left
       of the "@" sign is invalid.  This code is only useful for
       permanent failures.
    X.1.2   Bad destination system address
       The destination system specified in the address does not exist
       or is incapable of accepting mail.  For Internet mail names,
       this means the address portion to the right of the "@" is
       invalid for mail.  This code is only useful for permanent
       failures.
    X.1.3   Bad destination mailbox address syntax
       The destination address was syntactically invalid.  This can
       apply to any field in the address.  This code is only useful
       for permanent failures.
    X.1.4   Destination mailbox address ambiguous
       The mailbox address as specified matches one or more recipients
       on the destination system.  This may result if a heuristic
       address mapping algorithm is used to map the specified address
       to a local mailbox name.
    X.1.5   Destination address valid
       This mailbox address as specified was valid.  This status code
       should be used for positive delivery reports.

Vaudreuil Standards Track [Page 6] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.1.6   Destination mailbox has moved, No forwarding address
       The mailbox address provided was at one time valid, but mail is
       no longer being accepted for that address.  This code is only
       useful for permanent failures.
    X.1.7   Bad sender's mailbox address syntax
       The sender's address was syntactically invalid.  This can apply
       to any field in the address.
    X.1.8   Bad sender's system address
       The sender's system specified in the address does not exist or
       is incapable of accepting return mail.  For domain names, this
       means the address portion to the right of the "@" is invalid
       for mail.

3.3 Mailbox Status

    X.2.0   Other or undefined mailbox status
       The mailbox exists, but something about the destination mailbox
       has caused the sending of this DSN.
    X.2.1   Mailbox disabled, not accepting messages
       The mailbox exists, but is not accepting messages.  This may be
       a permanent error if the mailbox will never be re-enabled or a
       transient error if the mailbox is only temporarily disabled.
    X.2.2   Mailbox full
       The mailbox is full because the user has exceeded a per-mailbox
       administrative quota or physical capacity.  The general
       semantics implies that the recipient can delete messages to
       make more space available.  This code should be used as a
       persistent transient failure.
    X.2.3   Message length exceeds administrative limit
       A per-mailbox administrative message length limit has been
       exceeded.  This status code should be used when the per-mailbox
       message length limit is less than the general system limit.
       This code should be used as a permanent failure.

Vaudreuil Standards Track [Page 7] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.2.4   Mailing list expansion problem
       The mailbox is a mailing list address and the mailing list was
       unable to be expanded.  This code may represent a permanent
       failure or a persistent transient failure.

3.4 Mail system status

    X.3.0   Other or undefined mail system status
       The destination system exists and normally accepts mail, but
       something about the system has caused the generation of this
       DSN.
    X.3.1   Mail system full
       Mail system storage has been exceeded.  The general semantics
       imply that the individual recipient may not be able to delete
       material to make room for additional messages.  This is useful
       only as a persistent transient error.
    X.3.2   System not accepting network messages
       The host on which the mailbox is resident is not accepting
       messages.  Examples of such conditions include an immanent
       shutdown, excessive load, or system maintenance.  This is
       useful for both permanent and persistent transient errors.
    X.3.3   System not capable of selected features
       Selected features specified for the message are not supported
       by the destination system.  This can occur in gateways when
       features from one domain cannot be mapped onto the supported
       feature in another.
    X.3.4   Message too big for system
       The message is larger than per-message size limit.  This limit
       may either be for physical or administrative reasons.  This is
       useful only as a permanent error.
    X.3.5 System incorrectly configured
       The system is not configured in a manner that will permit it to
       accept this message.

Vaudreuil Standards Track [Page 8] RFC 3463 Enhanced Mail System Status Codes January 2003

3.5 Network and Routing Status

    X.4.0   Other or undefined network or routing status
       Something went wrong with the networking, but it is not clear
       what the problem is, or the problem cannot be well expressed
       with any of the other provided detail codes.
    X.4.1   No answer from host
       The outbound connection attempt was not answered, because
       either the remote system was busy, or was unable to take a
       call.  This is useful only as a persistent transient error.
    X.4.2   Bad connection
       The outbound connection was established, but was unable to
       complete the message transaction, either because of time-out,
       or inadequate connection quality.  This is useful only as a
       persistent transient error.
    X.4.3   Directory server failure
       The network system was unable to forward the message, because a
       directory server was unavailable.  This is useful only as a
       persistent transient error.
       The inability to connect to an Internet DNS server is one
       example of the directory server failure error.
    X.4.4   Unable to route
       The mail system was unable to determine the next hop for the
       message because the necessary routing information was
       unavailable from the directory server.  This is useful for both
       permanent and persistent transient errors.
       A DNS lookup returning only an SOA (Start of Administration)
       record for a domain name is one example of the unable to route
       error.
    X.4.5   Mail system congestion
       The mail system was unable to deliver the message because the
       mail system was congested.  This is useful only as a persistent
       transient error.

Vaudreuil Standards Track [Page 9] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.4.6   Routing loop detected
       A routing loop caused the message to be forwarded too many
       times, either because of incorrect routing tables or a user-
       forwarding loop.  This is useful only as a persistent transient
       error.
    X.4.7   Delivery time expired
       The message was considered too old by the rejecting system,
       either because it remained on that host too long or because the
       time-to-live value specified by the sender of the message was
       exceeded.  If possible, the code for the actual problem found
       when delivery was attempted should be returned rather than this
       code.

3.6 Mail Delivery Protocol Status

    X.5.0   Other or undefined protocol status
       Something was wrong with the protocol necessary to deliver the
       message to the next hop and the problem cannot be well
       expressed with any of the other provided detail codes.
    X.5.1   Invalid command
       A mail transaction protocol command was issued which was either
       out of sequence or unsupported.  This is useful only as a
       permanent error.
    X.5.2   Syntax error
       A mail transaction protocol command was issued which could not
       be interpreted, either because the syntax was wrong or the
       command is unrecognized.  This is useful only as a permanent
       error.
    X.5.3   Too many recipients
       More recipients were specified for the message than could have
       been delivered by the protocol.  This error should normally
       result in the segmentation of the message into two, the
       remainder of the recipients to be delivered on a subsequent
       delivery attempt.  It is included in this list in the event
       that such segmentation is not possible.

Vaudreuil Standards Track [Page 10] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.5.4   Invalid command arguments
       A valid mail transaction protocol command was issued with
       invalid arguments, either because the arguments were out of
       range or represented unrecognized features.  This is useful
       only as a permanent error.
    X.5.5   Wrong protocol version
       A protocol version mis-match existed which could not be
       automatically resolved by the communicating parties.

3.7 Message Content or Message Media Status

    X.6.0   Other or undefined media error
       Something about the content of a message caused it to be
       considered undeliverable and the problem cannot be well
       expressed with any of the other provided detail codes.
    X.6.1   Media not supported
       The media of the message is not supported by either the
       delivery protocol or the next system in the forwarding path.
       This is useful only as a permanent error.
    X.6.2   Conversion required and prohibited
       The content of the message must be converted before it can be
       delivered and such conversion is not permitted.  Such
       prohibitions may be the expression of the sender in the message
       itself or the policy of the sending host.
    X.6.3   Conversion required but not supported
       The message content must be converted in order to be forwarded
       but such conversion is not possible or is not practical by a
       host in the forwarding path.  This condition may result when an
       ESMTP gateway supports 8bit transport but is not able to
       downgrade the message to 7 bit as required for the next hop.
    X.6.4   Conversion with loss performed
       This is a warning sent to the sender when message delivery was
       successfully but when the delivery required a conversion in
       which some data was lost.  This may also be a permanent error
       if the sender has indicated that conversion with loss is
       prohibited for the message.

Vaudreuil Standards Track [Page 11] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.6.5   Conversion Failed
       A conversion was required but was unsuccessful.  This may be
       useful as a permanent or persistent temporary notification.

3.8 Security or Policy Status

    X.7.0   Other or undefined security status
       Something related to security caused the message to be
       returned, and the problem cannot be well expressed with any of
       the other provided detail codes.  This status code may also be
       used when the condition cannot be further described because of
       security policies in force.
    X.7.1   Delivery not authorized, message refused
       The sender is not authorized to send to the destination.  This
       can be the result of per-host or per-recipient filtering.  This
       memo does not discuss the merits of any such filtering, but
       provides a mechanism to report such.  This is useful only as a
       permanent error.
    X.7.2   Mailing list expansion prohibited
       The sender is not authorized to send a message to the intended
       mailing list.  This is useful only as a permanent error.
    X.7.3   Security conversion required but not possible
       A conversion from one secure messaging protocol to another was
       required for delivery and such conversion was not possible.
       This is useful only as a permanent error.
    X.7.4   Security features not supported
       A message contained security features such as secure
       authentication that could not be supported on the delivery
       protocol.  This is useful only as a permanent error.
    X.7.5   Cryptographic failure
       A transport system otherwise authorized to validate or decrypt
       a message in transport was unable to do so because necessary
       information such as key was not available or such information
       was invalid.

Vaudreuil Standards Track [Page 12] RFC 3463 Enhanced Mail System Status Codes January 2003

    X.7.6   Cryptographic algorithm not supported
       A transport system otherwise authorized to validate or decrypt
       a message was unable to do so because the necessary algorithm
       was not supported.
    X.7.7   Message integrity failure
       A transport system otherwise authorized to validate a message
       was unable to do so because the message was corrupted or
       altered.  This may be useful as a permanent, transient
       persistent, or successful delivery code.

4. Normative References

 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.
 [SMTP]    Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
           821, August 1982.
 [DSN]     Moore, K. and G. Vaudreuil, "An Extensible Message Format
           for Delivery Status Notifications", RFC 3464, January 2003.

5. Security Considerations

 This document describes a status code system with increased
 precision.  Use of these status codes may disclose additional
 information about how an internal mail system is implemented beyond
 that currently available.

Vaudreuil Standards Track [Page 13] RFC 3463 Enhanced Mail System Status Codes January 2003

Appendix A - Collected Status Codes

       X.1.0     Other address status
       X.1.1     Bad destination mailbox address
       X.1.2     Bad destination system address
       X.1.3     Bad destination mailbox address syntax
       X.1.4     Destination mailbox address ambiguous
       X.1.5     Destination mailbox address valid
       X.1.6     Mailbox has moved
       X.1.7     Bad sender's mailbox address syntax
       X.1.8     Bad sender's system address
       X.2.0     Other or undefined mailbox status
       X.2.1     Mailbox disabled, not accepting messages
       X.2.2     Mailbox full
       X.2.3     Message length exceeds administrative limit.
       X.2.4     Mailing list expansion problem
       X.3.0     Other or undefined mail system status
       X.3.1     Mail system full
       X.3.2     System not accepting network messages
       X.3.3     System not capable of selected features
       X.3.4     Message too big for system
       X.4.0     Other or undefined network or routing status
       X.4.1     No answer from host
       X.4.2     Bad connection
       X.4.3     Routing server failure
       X.4.4     Unable to route
       X.4.5     Network congestion
       X.4.6     Routing loop detected
       X.4.7     Delivery time expired
       X.5.0     Other or undefined protocol status
       X.5.1     Invalid command
       X.5.2     Syntax error
       X.5.3     Too many recipients
       X.5.4     Invalid command arguments
       X.5.5     Wrong protocol version
       X.6.0     Other or undefined media error
       X.6.1     Media not supported
       X.6.2     Conversion required and prohibited
       X.6.3     Conversion required but not supported
       X.6.4     Conversion with loss performed
       X.6.5     Conversion failed

Vaudreuil Standards Track [Page 14] RFC 3463 Enhanced Mail System Status Codes January 2003

       X.7.0     Other or undefined security status
       X.7.1     Delivery not authorized, message refused
       X.7.2     Mailing list expansion prohibited
       X.7.3     Security conversion required but not possible
       X.7.4     Security features not supported
       X.7.5     Cryptographic failure
       X.7.6     Cryptographic algorithm not supported
       X.7.7     Message integrity failure

Appendix B - Changes from RFC1893

 Changed Authors contact information.
 Updated required standards boilerplate.
 Edited the text to make it spell-checker and grammar checker
 compliant.
 Modified the text describing the persistent transient failure to more
 closely reflect current practice and understanding.
 Eliminated the restriction on the X.4.7 codes limiting them to
 persistent transient errors.

Author's Address

 Gregory M. Vaudreuil
 Lucent Technologies
 7291 Williamson Rd
 Dallas, Tx. 75214
 Phone: +1 214 823 9325
 EMail: GregV@ieee.org

Vaudreuil Standards Track [Page 15] RFC 3463 Enhanced Mail System Status Codes January 2003

Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS 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.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Vaudreuil Standards Track [Page 16]

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