📄 rfc1893.txt
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Network Working Group G. Vaudreuil
Request for Comments: 1893 Octel Network Services
Category: Standards Track January 1996
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.
1. Overview
There currently is not a standard mechanism for the reporting of mail
system errors except for 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 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 each 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
Vaudreuil Standards Track [Page 1]
RFC 1893 Mail System Status Codes January 1996
space for delivery notification reporting will reduce the available
codes for new ESMTP extensions.
The following proposal 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.
2. Status Codes
This document defines a new set of status codes to report mail system
conditions. These status codes are intended to be 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.
The codes 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 2]
RFC 1893 Mail System Status Codes January 1996
The class sub-code provides a broad classification of the status.
The enumerated values the class are defined as:
2.X.X Success
Success specifies that the DSN is reporting a positive delivery
action. Detail sub-codes may provide notification of
transformations required for delivery.
4.X.X Persistent Transient Failure
A persistent transient failure is one in which the message as
sent is valid, but some temporary event prevents the successful
sending of the message. Sending in the future may be successful.
5.X.X 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.X Other or Undefined Status
There is no additional subject information available.
X.1.X 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.X Mailbox Status
Mailbox status indicates that something having to do with the
mailbox has cause this DSN. Mailbox issues are assumed to be
under the general control of the recipient.
Vaudreuil Standards Track [Page 3]
RFC 1893 Mail System Status Codes January 1996
X.3.X 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.X 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.X 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. Mail
delivery protocol issues may be controlled by many parties
including the originating system, destination system, or
intermediate system administrators.
X.6.X 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 whom must support a common set of supported
content-types.
X.7.X 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.
Vaudreuil Standards Track [Page 4]
RFC 1893 Mail System Status Codes January 1996
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.
Vaudreuil Standards Track [Page 5]
RFC 1893 Mail System Status Codes January 1996
X.1.5 Destination address valid
This mailbox address as specified was valid. This status
code should be used for positive delivery reports.
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.
Vaudreuil Standards Track [Page 6]
RFC 1893 Mail System Status Codes January 1996
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.
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.
Vaudreuil Standards Track [Page 7]
RFC 1893 Mail System Status Codes January 1996
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 which will permit
it to accept this message.
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.
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