INTERNET-DRAFT C. Lindsey DKIM Working Group University of Manchester Intended status: Informational September 15, 2010 DKIM, MLMs and From Abstract It is proposed that a Mailing List Manager (MLM) may, under certain circumstances, replace the From header field of a message before forwarding it in order to prevent its being discarded by over-zealous DKIM verifiers/receivers. 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 March 15th, 2011. Copyright Notice Copyright (c) 2010 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. Table of Contents 1. Introduction .................................................. 2 2. The Proposal .................................................. 2 3. Normative References .......................................... 4 4. AUthor's Address .............................................. 4 C. H. Lindsey [Page 1] Internet-Draft DKIM, MLMs and From September 15, 2010 1. Introduction This memo is to be read in conjunction with [KUCHERAWY]. Readers are presumed to be familiar with that document and with the terminology used therein. [KUCHERAWY] describes some problems which can arise when a mail message is DKIM-signed by a domain which has declared a strict policy such as "discardable", and gives advice on how to deal with these problems. This memo proposes an additional tool whereby the MLM replaces the From header field with a variant that will not cause the forwarded message to be discarded by subsequent agents on the grounds that it contains no signature from the originating domain. The tool is described by way of additional text which it is proposed should be added to [KUCHERAWY]. 2. The Proposal Within [KUCHERAWY], add a new section 5.2.1 (or alternatively a new section 5.3, with the subsequent sections renumbered), containing the following text: START OF ADDITIONAL TEXT Nevertheless, this document is only advisory, and an MLM may be faced with an originating ADMD that declines to divide its messages into appropriate streams (2.5), each with an appropriate ADSP policy; or with an author who is not permitted to create any extra stream (5.4); or with a receiver that is unwilling to accept his signed [AUTH_RESULTS] header field. Moreover, having regard to the importance of getting messages transmitted reliably to all recipients on his list, an MLM may be unwilling to accept the advice to reject certain mail outright (5.2). In that case (and only for messages signed by domains declaring a strict ADSP policy and for which he is about to invalidate the existing signature) he may change the From header field on the message to contain his own domain in its (i.e. after the '@'). This will surely prevent discarding of the message on account of that strict ADSP policy, but it must be regarded as a "method of last resort" since it can raise further difficulties (see below). Moreover, it must be used with a signed [AUTH_RESULTS] header field (5.6 and 5.7). In order that recipients will still recognize the message as coming from the original author, any in the original From header field should be retained (or possibly augmented), and the original should be somehow encoded in the new . It is recommended that this be done by means of the "percent hack" which is nowadays normally deprecated, but is still implemented (when so C. H. Lindsey [Page 2] Internet-Draft DKIM, MLMs and From September 15, 2010 configured) in several current MTAs. For example, the oreiginal From header field From: Joe Doe would be replaced by From: Joe Doe Moreover, except where the original author had provided some Reply-To header field, or where the policy of the MLM was to provide a Reply- To pointing to the list submission address, the MLM should insert a new Reply-To taken from the original From header field, e.g.: Reply-To: Joe Doe Nevertheless, any MLM who chooses to adopt this technique needs to accept some additional responsibilities, and to be aware of some problems: 1. He should implement the percent hack so that replies sent to the new From header field (especially where no Reply-To header field could be inserted) will be forwarded by the MLM to the original author. 2. He should refrain from forwarding to addresses for which he has not previously created a new From header field, otherwise he will have created an "open relay". 3. This is especially hard to do for lists which accept messages from non-subscribers (how long should he continue to forward to such occasional authors?) Even when submission is restricted to list subscribers, he still has to decide how long to continue to forward to them after they have unsubscribed. 4, Recipeints on the list will be faced with some From header fields in an unfamiliar (percentified) format, though generating a reply address by hand is not difficult once one has twigged the notation. 5. Percentified addresses (which may later cease to work) may get written into users' address books. Moreover, a given author may get listed in the address book twice, in both its percentified an unpercentified forms. For these reasons, an MLM must weigh the advantages and disadvantages very carefully before adopting this protocol. END OF ADDITIONAL TEXT Some further small changes to [KUCHERAWY] are also proposed: C. H. Lindsey [Page 3] Internet-Draft DKIM, MLMs and From September 15, 2010 1. In 1.4, change the last sentence of the first paragraph to read: An attempt has been made to prefer imposing changes to behaviour at the signer and verifier rather than at the MLM, though the MLM may have to fix matters himself if faced with uncooperative signers or verifiers. 2. In 3.3, under "Other header fields:", after the first sentence, insert Even the "From" may sometines be replaced (5.2.1). 3. Normative References [KUCHERAWY] "DKIM And Mailing Lists", draft-ietf-dkim-mailinglists- 02, August 10, 2010. 4. AUthor's Address Charles. H. Lindsey 5 Clerewood Avenue Heald Green Cheadle Cheshire SK8 3JU United Kingdom Phone: +44 161 436 6131 Email: chl@clerew.man.ac.uk Comments on this draft should be sent to the mailing list of the DKIM Working Group at ietf-dkim@mipassoc.org C. H. Lindsey [Page 4]