Network Working Group Arnt Gulbrandsen Internet-Draft March 2012 Intended Status: Proposed Standard EAI: Simplified POP/IMAP downgrading draft-ietf-eai-simpledowngrade-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Copyright (c) 2012 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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet- Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft expires in September 2012. Gulbrandsen Expires August 2012 [Page 1] Internet-draft June 2011 Abstract This document specifies a method for IMAP and POP servers to serve EAI messages to non-EAI clients. The specification is simple, easy to implement and provides only rudimentary results. 1. Overview It may happen that an EAI-ignorant IMAP or POP client opens a mailbox containing EAI messages, or even read EAI messages, for instance when a user has both EAI-capable and EAI-ignorant MUAs. While the server can hide the existence of such messages entirely, doing that can be both tricky to implement and not very friendly to the user. This document specifies a way to present such messages to the client. It values simplicity of implementation over fidelity of representation, on the theory that anyone who wants accuracy should use EAI, and implementers' time should be used for implementing EAI proper. The server is assumed to be EAI-capable internally. When it needs to present an EAI message (the "real message") to a non-EAI client, it synthesizes a non-EAI message containing most of the information and presents that (the "synthetic message"). 2. Information preserved and lost The synthetic message is intended to convey the most important information to the user. Where information is lost, the user should see the message as incomplete rather than modified. The synthetic message is not intended to convey any EAI information to the MUA. Nothing parsable is added. 2.1 Email addresses Each regular EAI-specific email address in the 14 header fields listed below is replaced with an invalid email address whose display- name tells the user what happened. The format of the display-name is explicitly unspecified. Given an EAI address "Fred ", the rendering might Gulbrandsen Expires August 2012 [Page 2] Internet-draft June 2011 be "fred@EXAMPLE.com " or "Fred ". Irregular email addresses (anything to which one cannot send mail, such as "unknown:;") are silently excised. The affected header fields are Bcc, Cc, From, ReplyTo, ResentBcc, ResentCc, ResentFrom, ResentSender, ResentTo, ReturnPath, Sender and To. Any addresses present in other header fields are not regarded as addresses by this specification. 2.2 Mime values and comments Any mime field (whether in the message header or a bodypart header) which cannot be presented as-is to the client is silently excised along with its name. Given a field such as "Content-Disposition: attachment; filename=foo; signed-off-by=fred@EXAMPLE.com", the field is presented as "Content- Disposition: attachment; filename=foo". 2.3 Remaining header fields Any header field which cannot be presented to the client even after the modifications in sections 3.1 and 3.2 is silently excised. 3. IMAP-specific details IMAP offers a way to retrieve the message size without downloading it, RFC822.SIZE. [RFC3501] requires that this size be exactly correct. This specification relaxes that requirement: An IMAP server is permitted to send the size of the real message as RFC822.SIZE, even though the synthetic message's size differs. 4. POP-specific details None appear to be needed. 6. Security Considerations If the real message contains signed body parts, the synthetic message Gulbrandsen Expires August 2012 [Page 3] Internet-draft June 2011 may contain an invalid signature. If any excised information is significant, then that information does not arrive at the recipient. Notably, the message-id, in-reference-to and/or references fields may be excised, which might cause a lack of context when the recipient reads the message. 8. Acknowledgements John Levine and Kazunori Fujiwara helped with this document. I think a third person did too, but cannot find the relevant mail. Speak up or be forgotten. 9. Normative References [RFC3501] Crispin, "Internet Message Access Protocol - Version 4rev1", RFC 3501, University of Washington, June 2003. 10. Author's Address Arnt Gulbrandsen Schweppermannstr. 8 D-81671 Muenchen Germany Fax: +49 89 4502 9758 Email: arnt@gulbrandsen.priv.no Gulbrandsen Expires August 2012 [Page 4] Internet-draft June 2011 (RFC Editor: Please delete everything after this point) IANA Considerations This document has no actions for IANA. Open Issues Only those noted as "fixme" in the text. Changes since -00 Gulbrandsen Expires August 2012 [Page 5]