Internet DRAFT - draft-ietf-822ext-smtperror
draft-ietf-822ext-smtperror
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Network Working Group Ned Freed, Innosoft
Internet Draft <draft-ietf-822ext-smtperror-00.txt>
SMTP Service Extension for
Returning Enhanced Error Codes
March 1996
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are
working documents of the Internet Engineering Task Force
(IETF), its areas, and its working groups. Note that other
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1. Abstract
This memo defines an extension to the SMTP service [RFC-821,
RFC-1869] whereby an SMTP server augments its responses with
the enhanced mail system status codes defined in RFC 1893.
These codes can then be used to provide more informative
explanations of error conditions, especially in the context of
the delivery status notifications format defined in RFC 1894.
2. Introduction
Although SMTP is widely and robustly deployed, various
extensions have been requested by parts of the Internet
Internet Draft SMTP Enhanced Error Codes March 1996
community. In particular, in the modern, international, and
multilingual Internet a need exists to assign codes to
specific error conditions that can be translated into
different languages. RFC 1893 defines such a set of status
codes and RFC 1894 defines a mechanism to send such coded
material to users. However, in many cases the agent creating
the RFC 1894 delivery status notification is doing so in
response to errors it received from a remote SMTP server.
As such, remote servers need a mechanism for embedding
enhanced status codes in their responses as well as a way to
indicate to a client when they are in fact doing this. This
memo uses the SMTP extension mechanism described in RFC 1869
to define such a mechanism.
3. Framework for the Enhanced Error Statuses Extension
The enhanced error statuses transport extension is laid out as
follows:
(1) the name of the SMTP service extension defined here is
Enhanced-Status-Codes;
(2) the EHLO keyword value associated with the extension is
ENHANCEDSTATUSCODES;
(3) no parameter is used with the ENHANCEDSTATUSCODES EHLO
keyword;
(4) the text part of all 2xx, 4xx, and 5xx SMTP responses
other than the initial greeting and any response to
HELO or EHLO are prefaced with a status code as defined
in RFC 1893. This status code is always followed by one
or more spaces.
(5) no additional SMTP verbs are defined by this extension;
and,
(6) the next section specifies how support for the
extension affects the behavior of a server and client
SMTP.
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Internet Draft SMTP Enhanced Error Codes March 1996
4. The Enhanced-Status-Codes service extension
Servers supporting the Enhanced-Status-Codes extension must
preface the text part of almost all response lines with a
status code. As in RFC 1893, the syntax of these status codes
is given by the ABNF:
status-code ::= class "." subject "." detail
class ::= "2" / "4" / "5"
subject ::= 1*3digit
detail ::= 1*3digit
These codes must appear in all 2xx, 4xx, and 5xx response
lines other than initial greeting and any response to HELO or
EHLO. Note that 3xx responses are NOT included in this list.
All status codes returned by the server must agree with the
primary response code, that is, a 2xx response must
incorporate a 2.X.X code, a 4xx response must incorporate a
4.X.X code, and a 5xx response must incorporate a 5.X.X code.
When responses are continued across multiple lines the same
status code must appear at the beginning of the text in each
line of the response.
Servers supporting this extension must attach enhanced status
codes to their responses regardless of whether or not EHLO is
employed by the client.
5. Usage Example
The following dialogue illustrates the use of enhanced status
codes by a server:
S: <wait for connection on TCP port 25>
C: <open connection to server>
S: 220 dbc.mtview.ca.us SMTP service ready
C: EHLO ymir.claremont.edu
S: 250-dbc.mtview.ca.us says hello
S: 250 ENHANCEDSTATUSCODES
C: MAIL FROM:<ned@ymir.claremont.edu>
S: 250 2.1.0 Originator <ned@ymir.claremont.edu> ok
C: RCPT TO:<mrose@dbc.mtview.ca.us>
S: 250 2.1.5 Recipient <mrose@dbc.mtview.ca.us> ok
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Internet Draft SMTP Enhanced Error Codes March 1996
C: RCPT TO:<nosuchuser@dbc.mtview.ca.us>
S: 550 5.1.1 Mailbox "nosuchuser" does not exist
C: RCPT TO:<remoteuser@isi.edu>
S: 551-5.7.1 Forwarding to remote hosts disabled
S: 551 5.7.1 Select another host to act as your forwarder
C: DATA
S: 354 Send message, ending in CRLF.CRLF.
...
C: .
S: 250 2.6.0 Message accepted
C: QUIT
S: 221 2.0.0 Goodbye
The client that receives these responses might then send a
nondelivery notification of the general form:
Date: Mon, 11 Mar 1996 09:21:47 -0400
From: Mail Delivery Subsystem <mailer-daemon@ymir.claremont.edu>
Subject: Returned mail
To: <ned@ymir.claremont.edu>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary="JAA13167.773673707/YMIR.CLAREMONT.EDU"
--JAA13167.773673707/YMIR.CLAREMONT.EDU
content-type: text/plain; charset=us-ascii
----- Mail was successfully relayed to
the following addresses -----
<mrose@dbc.mtview.ca.us>
----- The following addresses had delivery problems -----
<nosuchuser@dbc.mtview.ca.us>
(Mailbox "nosuchuser" does not exist)
<remoteuser@isi.edu>
(Forwarding to remote hosts disabled)
--JAA13167.773673707/YMIR.CLAREMONT.EDU
content-type: message/delivery-status
Reporting-MTA: dns; ymir.claremont.edu
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Internet Draft SMTP Enhanced Error Codes March 1996
Original-Recipient: rfc822;mrose@dbc.mtview.ca.us
Final-Recipient: rfc822;mrose@dbc.mtview.ca.us
Action: relayed
Status: 2.1.5 (Destination address valid)
Diagnostic-Code: smtp;
250 Recipient <mrose@dbc.mtview.ca.us> ok
Remote-MTA: dns; dbc.mtview.ca.us
Original-Recipient: rfc822;nosuchuser@dbc.mtview.ca.us
Final-Recipient: rfc822;nosuchuser@dbc.mtview.ca.us
Action: failed
Status: 5.1.1 (Bad destination mailbox address)
Diagnostic-Code: smtp;
550 Mailbox "nosuchuser" does not exist
Remote-MTA: dns; dbc.mtview.ca.us
Original-Recipient: rfc822;remoteuser@isi.edu
Final-Recipient: rfc822;remoteuser@isi.edu
Action: failed
Status: 5.7.1 (Delivery not authorized, message refused)
Diagnostic-Code: smtp;
551 Forwarding to remote hosts disabled
Select another host to act as your forwarder
Remote-MTA: dns; dbc.mtview.ca.us
--JAA13167.773673707/YMIR.CLAREMONT.EDU
content-type: message/rfc822
[original message goes here]
--JAA13167.773673707/YMIR.CLAREMONT.EDU--
Note that in order to reduce clutter the reporting MTA has
omitted enhanced status code information from the
diagnostic-code fields it has generated.
6. Security Considerations
Additional detail in server responses axiomatically provides
additional information about the server. It is conceivable
that additional information of this sort may be of assistance
in circumventing server security. The advantages of provides
additional information must always be weighed against the
security implications of doing so.
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7. References
[RFC-821]
Postel, J., "Simple Mail Transfer Protocol", RFC 821,
August, 1982. (August, 1982).
[RFC-1869]
Rose, M., Stefferud, E., Crocker, C., Klensin, J., Freed,
N., "SMTP Service Extensions", RFC 1869, November, 1995.
[RFC-1893]
Vaudreuil, G., "Enhanced Mail System Status Codes", RFC
1893, January, 1996.
[RFC-1894]
Moore, K., Vaudreuil, G., "An Extensible Message Format
for Delivery Status Notifications", RFC 1894, January,
1996.
8. Author Address
Ned Freed
Innosoft International, Inc.
1050 East Garvey Avenue South
West Covina, CA 91790
USA
tel: +1 818 919 3600 fax: +1 818 919 3614
email: ned@innosoft.com
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