Internet DRAFT - draft-ietf-appsawg-email-auth-codes
draft-ietf-appsawg-email-auth-codes
Network Working Group M. Kucherawy
Internet-Draft August 8, 2014
Updates: 7208 (if approved)
Intended status: Standards Track
Expires: February 9, 2015
Email Authentication Status Codes
draft-ietf-appsawg-email-auth-codes-07
Abstract
This document registers code points to allow status codes to be
returned to an email client to indicate that a message is being
rejected or deferred specifically because of email authentication
failures.
This document updates [RFC7208] since some of the code points
registered replace the ones recommended for use in that document.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 9, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Kucherawy Expires February 9, 2015 [Page 1]
Internet-Draft Email Auth Status Codes August 2014
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New Enhanced Status Codes . . . . . . . . . . . . . . . . . . . 3
3.1. DKIM Failure Codes . . . . . . . . . . . . . . . . . . . . 3
3.2. SPF Failure Codes . . . . . . . . . . . . . . . . . . . . . 4
3.3. Reverse DNS Failure Code . . . . . . . . . . . . . . . . . 5
3.4. Multiple Authentication Failures Code . . . . . . . . . . . 5
4. General Considerations . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 7
Kucherawy Expires February 9, 2015 [Page 2]
Internet-Draft Email Auth Status Codes August 2014
1. Introduction
[RFC3463] introduced Enhanced Mail System Status Codes, and [RFC5248]
created an IANA registry for these.
[RFC6376] and [RFC7208] introduced, respectively, DomainKeys
Identified Mail (DKIM) and Sender Policy Framework (SPF), two
protocols for conducting message authentication. Another common
email acceptance test is the reverse Domain Name System (DNS) check
on an email client's IP address, as described in Section 3 of
[RFC7001].
The current set of enhanced status codes does not include any code
for indicating that a message is being rejected or deferred due to
local policy reasons related to any of these mechanisms. This is
potentially useful information to agents that need more than
rudimentary handling information about the reason a message was
rejected on receipt. This document introduces enhanced status codes
for reporting those cases to clients.
Section 3.2 updates [RFC7208], as new enhanced status codes relevant
to that specification are being registered and recommended for use.
2. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
3. New Enhanced Status Codes
The following new enhanced status codes are defined:
3.1. DKIM Failure Codes
In the code point definitions below, the following definitions are
used:
passing: A signature is "passing" if the basic DKIM verification
algorithm as defined in [RFC6376] succeeds.
acceptable: A signature is "acceptable" if it satisfies all locally
defined requirements (if any) in addition to passing the basic
DKIM verification algorithm (e.g., certain header fields are
included in the signed content; no partial signatures; etc.).
Kucherawy Expires February 9, 2015 [Page 3]
Internet-Draft Email Auth Status Codes August 2014
Code: X.7.20
Sample Text: No passing DKIM signature found
Associated basic status code: 550
Description: This status code is returned when a message
did not contain any passing DKIM
signatures. (This violates the
advice of Section 6.1 of RFC6376.)
Reference: [this document]; RFC6376
Submitter: M. Kucherawy
Change controller: IESG
Code: X.7.21
Sample Text: No acceptable DKIM signature found
Associated basic status code: 550
Description: This status code is returned when a message
contains one or more passing DKIM signatures,
but none are acceptable. (This violates the
advice of Section 6.1 of RFC6376.)
Reference: [this document]; RFC6376
Submitter: M. Kucherawy
Change controller: IESG
Code: X.7.22
Sample Text: No valid author-matched DKIM signature found
Associated basic status code: 550
Description: This status code is returned when a message
contains one or more passing DKIM
signatures, but none are acceptable because
none have an identifier(s)
that matches the author address(es) found in
the From header field. This is a special
case of X.7.21. (This violates the advice
of Section 6.1 of RFC6376.)
Reference: [this document]; RFC6376
Submitter: M. Kucherawy
Change controller: IESG
3.2. SPF Failure Codes
Kucherawy Expires February 9, 2015 [Page 4]
Internet-Draft Email Auth Status Codes August 2014
Code: X.7.23
Sample Text: SPF validation failed
Associated basic status code: 550
Description: This status code is returned when a message
completed an SPF check that produced a
"fail" result, contrary to local policy
requirements. Used in place of 5.7.1 as
described in Section 8.4 of RFC7208.
Reference: [this document]; RFC7208
Submitter: M. Kucherawy
Change controller: IESG
Code: X.7.24
Sample Text: SPF validation error
Associated basic status code: 451/550
Description: This status code is returned when evaluation
of SPF relative to an arriving message
resulted in an error. Used in place of
4.4.3 or 5.5.2 as described in Sections
8.6 and 8.7 of RFC7208.
Reference: [this document]; RFC7208
Submitter: M. Kucherawy
Change controller: IESG
3.3. Reverse DNS Failure Code
Code: X.7.25
Sample Text: Reverse DNS validation failed
Associated basic status code: 550
Description: This status code is returned when an SMTP
client's IP address failed a reverse DNS
validation check, contrary to local policy
requirements.
Reference: [this document]; Section 3 of RFC7001
Submitter: M. Kucherawy
Change controller: IESG
3.4. Multiple Authentication Failures Code
Kucherawy Expires February 9, 2015 [Page 5]
Internet-Draft Email Auth Status Codes August 2014
Code: X.7.26
Sample Text: Multiple authentication checks failed
Associated basic status code: 550
Description: This status code is returned when a message
failed more than one message authentication
check, contrary to local policy requirements.
The specific mechanisms that failed are not
specified.
Reference: [this document]
Submitter: M. Kucherawy
Change controller: IESG
4. General Considerations
By the nature of the Simple Mail Transfer Protocol (SMTP), only one
enhanced status code can be returned for a given exchange between
client and server. However, an operator might decide to defer or
reject a message for a plurality of reasons. Clients receiving these
codes need to consider that the failure reflected by one of these
status codes might not reflect the only reason, or the most important
reason, for non-acceptance of the message or command.
It is important to note that Section 6.1 of [RFC6376] discourages
special treatment of messages bearing no valid DKIM signature. There
are some operators that disregard this advice, a few of which go so
far as to require a valid Author Domain signature (that is, one
matching the domain(s) in the From header field) in order to accept
the message. Moreover, some nascent technologies built atop SPF and
DKIM depend on such authentications. This work does not endorse
configurations that violate DKIM's recommendations, but rather
acknowledges that they do exist and merely seeks to provide for
improved interoperability with such operators.
A specific use case for these codes is mailing list software, which
processes rejections in order to remove from the subscriber set those
addresses that are no longer valid. There is a need in that case to
distinguish authentication failures versus indications that the
recipient address is no longer valid.
If a receiving server performs multiple authentication checks, and
more than one of them fails thus warranting rejection of the message,
the SMTP server SHOULD use the code that indicates multiple methods
failed rather than only reporting the first one that failed. It may
be the case that one method is always expected to fail, and thus
returning that method's specific code is not information useful to
the sending agent.
The reverse IP DNS check is defined in Section 2.6.3 of [RFC7001].
Kucherawy Expires February 9, 2015 [Page 6]
Internet-Draft Email Auth Status Codes August 2014
Any message authentication or policy enforcement technologies
developed in the future should also include registration of their own
enhanced status codes so that this kind of specific reporting is
available to operators that wish to use them.
5. Security Considerations
Use of these codes reveals local policy with respect to email
authentication, which can be useful information to actors attempting
to deliver undesired mail. It should be noted that there is no
specific obligation to use these codes; if an operator wishes not to
reveal this aspect of local policy, it can continue using a generic
result code such as 5.7.7, 5.7.1, or even 5.7.0.
6. IANA Considerations
Registration of new enhanced status codes, for addition to the
Enumerated Stauts Codes sub-registry of the SMTP Enhanced Status
Codes Registry, can be found in Section 3.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, January 2003.
[RFC5248] Hansen, T. and J. Klensin, "A Registry for SMTP Enhanced
Mail System Status Codes", BCP 138, RFC 5248, June 2008.
[RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
Identified Mail (DKIM) Signatures", STD 76, RFC 6376,
September 2011.
[RFC7001] Kucherawy, M., "Message Header Field for Indicating
Message Authentication Status", RFC 7001, September 2013.
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for
Authorizing Use of Domains in Email, Version 1", RFC 7208,
April 2014.
Appendix A. Acknowledgments
Claudio Allocchio, Dave Crocker, Ned Freed, Arnt Gulbrandsen, Scott
Kitterman, Barry Leiba, Alexey Melnikov, S. Moonesamy, Hector Santos,
and Stephen Turnbull contributed to this work.
Kucherawy Expires February 9, 2015 [Page 7]
Internet-Draft Email Auth Status Codes August 2014
Author's Address
Murray S. Kucherawy
270 Upland Drive
San Francisco, CA 94127
USA
EMail: superuser@gmail.com
Kucherawy Expires February 9, 2015 [Page 8]
