Network Working Group Greg Vaudreuil
Internet Draft Octel Network Services
Expires: 11/5/1995 May 5, 1995
Enhanced Mail System Status Codes
<draft-ietf-notary-status-03.txt>
Status of this Memo
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Internet Draft Mail System Status Codes May 5, 1995
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 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.
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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.
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
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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.
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.
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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.
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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.
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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 domain
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 domain 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.
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.
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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 either because the user has exceeded an
administrative quota. 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 (3.0)
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.
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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 a user forwarding
loop. This is useful only as a persistent transient error.
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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. This is useful only as a persistent transient error.
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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.
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 downgrading one of the communicating
parties. This should never happen in ESMTP.
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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 the either the
delivery protocol or a host in the forwarding path. This is
useful only as a permanent error.
X.6.2 Conversion required and prohibited (6.2)
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 (6.3)
The message content must be converted 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 a relay supports
ESMTP transport but not MIME downgrade.
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.
X.6.5 Conversion Failed
A conversion was required but was unsuccessful. This may be
useful as a permanent or persistent temporary notification.
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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 which 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. This is useful only as a permanent error.
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., Vaudreuil, G., "An Extensible Message Format for
Delivery Status Notifications", Internet-Draft.
5. Security Consideration
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.
6. Acknowledgments
The author wishes to offer special thank Harald Alvestrand, Marko
Kaittola, and Keith Moore for their extensive review and
constructive suggestions.
7. Author's Address
Gregory M. Vaudreuil
Octel Network Services
17060 Dallas Parkway
Suite 214
Dallas, TX 75248-1905
Voice/Fax: +1-214-733-2722
Greg.Vaudreuil@Octel.com
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8. Appendix - 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
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
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X.7.7 Message integrity failure
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