Network Working Group M. Kucherawy Internet-Draft June 2, 2014 Intended status: Informational Expires: December 4, 2014 Email Authentication Status Codes draft-ietf-appsawg-email-auth-codes-02 Abstract There is at present no way to return a status code to an email client that indicates a message is being rejected or deferred specifically because of email authentication failures. This document registers codes for this purpose. 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 December 4, 2014. 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 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. Kucherawy Expires December 4, 2014 [Page 1] Internet-Draft Email Auth Status Codes June 2014 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. New Status Codes . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. DKIM Failure Codes . . . . . . . . . . . . . . . . . . . . 3 3.2. SPF Failure Codes . . . . . . . . . . . . . . . . . . . . . 4 3.3. Reverse DNS Failure Code . . . . . . . . . . . . . . . . . 4 3.4. Multiple Authentication Failures Code . . . . . . . . . . . 5 4. General Considerations . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 7 Kucherawy Expires December 4, 2014 [Page 2] Internet-Draft Email Auth Status Codes June 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 and Sender Policy Framework, two protocols for conducting email authentication. Another common email acceptance test is the reverse Domain Name System 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 either of these two 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. 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 Status Codes The following new status codes are defined: 3.1. DKIM Failure Codes Code: X.7.20 Sample Text: No valid DKIM signature found Associated basic status code: 5 Description: This status code is returned when a message did not contain a valid DKIM signature, contrary to local policy requirements. (Note that this violates the advice of Section 6.1 of RFC6376.) Reference: [this document]; RFC6376 Submitter: M. Kucherawy Change controller: IESG Kucherawy Expires December 4, 2014 [Page 3] Internet-Draft Email Auth Status Codes June 2014 Code: X.7.21 Sample Text: No valid author DKIM signature found Associated basic status code: 5 Description: This status code is returned when a message did not contain a valid DKIM signature matching the domain(s) found in the From header field, contrary to local policy requirements. (Note that 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 Code: X.7.22 Sample Text: SPF validation failed Associated basic status code: 5 Description: This status code is returned when a message failed an SPF check, contrary to local policy requirements. Reference: [this document]; RFC7208 Submitter: M. Kucherawy Change controller: IESG Code: X.7.23 Sample Text: SPF validation error Associated basic status code: 5 Description: This status code is returned when evaluation of SPF relative to an arriving message resulted in an error. Reference: [this document]; RFC7208 Submitter: M. Kucherawy Change controller: IESG 3.3. Reverse DNS Failure Code Kucherawy Expires December 4, 2014 [Page 4] Internet-Draft Email Auth Status Codes June 2014 Code: X.7.24 Sample Text: Reverse DNS validation failed Associated basic status code: 5 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 RFC 7001 Submitter: M. Kucherawy Change controller: IESG 3.4. Multiple Authentication Failures Code Code: X.7.25 Sample Text: Multiple authentication checks failed Associated basic status code: 5 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 signature. There are some operators that disregard this advice, a few of which go so far as to require a valid Author Domain signature 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 provides for improved interoperability with such operators. A specific use case is mailing list software, which processes rejections in order to remove from the subscriber set those addresses Kucherawy Expires December 4, 2014 [Page 5] Internet-Draft Email Auth Status Codes June 2014 that are no longer valid. There is a need in that case to distinguish authentication failures verus indications that the recipient address is no longer valid. When multiple authentication methods fail, the SMTP server SHOULD use the code that indicates multiple methods failed rather than only 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]. 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 undesirable 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 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. Kucherawy Expires December 4, 2014 [Page 6] Internet-Draft Email Auth Status Codes June 2014 Appendix A. Acknowledgments Claudio Allocchio, Ned Freed, Arnt Gulbrandsen, Scott Kitterman, Barry Leiba, Alexey Melnikov, and Hector Santos contributed to this work. Author's Address Murray S. Kucherawy 270 Upland Drive San Francisco, CA 94127 USA EMail: superuser@gmail.com Kucherawy Expires December 4, 2014 [Page 7]