Internet Draft Greg Vaudreuil
Expires in six months Lucent Technologies
April 16, 2002

Enhanced Mail System Status Codes

<draft-vaudreuil-1893bis-01.txt>

Status of this Memof

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026.

This document is an Internet Draft. Internet Drafts are working
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This Internet-Draft is in conformance with Section 10 of RFC 2026.

Abstract

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

Internet Draft Mail System Status Codes April 16, 2002

Working Group Summary

RFC 1893 was a product of the Notary working group. This document is
a revision of that document providing clarifications as necessary to
advance to draft standard.

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 RFC-2119 [RFC2119].

Table of Contents

1. OVERVIEW ..........................................................3
2. STATUS CODE STRUCTURE .............................................4
3. ENUMERATED STATUS CODES ...........................................7
3.1 Other or Undefined Status .......................................7
3.2 Address Status ..................................................7
3.3 Mailbox Status ..................................................8
3.4 Mail system status ..............................................9
3.5 Network and Routing Status .....................................10
3.6 Mail Delivery Protocol Status ..................................11
3.7 Message Content or Message Media Status ........................12
3.8 Security or Policy Status ......................................13
4. REFERENCES .......................................................15
5. SECURITY CONSIDERATIONS ..........................................15
6. COPYRIGHT NOTICE .................................................16
7. AUTHOR'S ADDRESS .................................................16
8. APPENDIX A - CHANGES FROM RFC1893 ................................17

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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 each. 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 partitioned in the number space 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.

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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.

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 some temporary event

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prevents the successful sending of the message. 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.

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

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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.

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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.

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 codes 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.

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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.

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.

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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
permanent 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.

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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, either
because the remote system was busy, or otherwise 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
otherwise 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.

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

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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. This is useful
only as a persistent transient error.

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.

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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.

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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.

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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.

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4. References

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

[DSN] Moore, K., and G. Vaudreuil, "An Extensible Message Format for
Delivery Status Notifications", RFC 1894, University of Tennessee,
Octel Network Services, January 1996.

[SMTP-CODES] G. Vaudreuil, " Enhanced Mail System Status Codes' ', RFC
1893, Octel Network Services, January 1996.

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.

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6. Copyright Notice

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."

7. Author's Address

Gregory M. Vaudreuil
Lucent Technologies
17080 Dallas Parkway
Dallas, TX 75248-1905
Voice/Fax: +1-972-733-2722
GregV@ieee.org

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8. 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

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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

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9. 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

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