Advice for Safe Handling of Malformed Messages
draft-ietf-appsawg-malformed-mail-06

The information below is for an old version of the document
Document Type Active Internet-Draft (appsawg WG)
Last updated 2013-06-18
Replaces draft-kucherawy-mta-malformed
Stream IETF
Intended RFC status Best Current Practice
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Stream WG state WG Document (wg milestone: Sep 2013 - Publication requeste... )
Document shepherd Salvatore Loreto
IESG IESG state I-D Exists (IESG: Dead)
Consensus Boilerplate Unknown
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Responsible AD Barry Leiba
Send notices to appsawg-chairs@tools.ietf.org, draft-ietf-appsawg-malformed-mail@tools.ietf.org
APPSAWG                                                     M. Kucherawy
Internet-Draft                                                G. Shapiro
Intended status: Informational                             June 18, 2013
Expires: December 20, 2013

             Advice for Safe Handling of Malformed Messages
                  draft-ietf-appsawg-malformed-mail-06

Abstract

   Although Internet mail formats have been precisely defined since the
   1970s, authoring and handling software often show only mild
   conformance to the specifications.  The distributed and non-
   interactive nature of email has often prompted adjustments to
   receiving software, to handle these variations, rather than trying to
   gain better conformance by senders, since the receiving operator is
   primarily driven by complaining recipient users and has no authority
   over the sending side of the system.  Processing with such
   flexibility comes at some cost, since mail software is faced with
   decisions about whether or not to permit non-conforming messages to
   continue toward their destinations unaltered, adjust them to conform
   (possibly at the cost of losing some of the original message), or
   outright rejecting them.

   A core requirement for interoperability is that both sides of an
   exchange work from the same details and semantics.  By having
   receivers be flexible, beyond the specifications, there can be -- and
   often has been -- a good chance that a message will not be fully
   interoperable.  Worse, a well-established pattern of tolerance for
   variations can sometimes be used as an attack vector.

   This document includes a collection of the best advice available
   regarding a variety of common malformed mail situations, to be used
   as implementation guidance.  It must be emphasized, however, that the
   intent of this document is not to standardize malformations or
   otherwise encourage their proliferation.  The messages are manifestly
   malformed, and the code and culture that generates them needs to be
   fixed.  Therefore, these messages should be rejected outright if at
   all possible.  Nevertheless, many malformed messages from otherwise
   legitimate senders are in circulation and will be for some time, and,
   unfortunately, commercial reality shows that we cannot always simply
   reject or discard them.  Accordingly, this document presents
   alternatives for dealing with them in ways that seem to do the least
   additional harm until the infrastructure is tightened up to match the
   standards.

Status of This Memo

Kucherawy & Shapiro     Expires December 20, 2013               [Page 1]
Internet-Draft             Safe Mail Handling                  June 2013

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on December 20, 2013.

Copyright Notice

   Copyright (c) 2013 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
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   described in the Simplified BSD License.

Kucherawy & Shapiro     Expires December 20, 2013               [Page 2]
Internet-Draft             Safe Mail Handling                  June 2013

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  The Purpose Of This Work . . . . . . . . . . . . . . . . .  4
     1.2.  Not The Purpose Of This Work . . . . . . . . . . . . . . .  4
     1.3.  General Considerations . . . . . . . . . . . . . . . . . .  5
   2.  Document Conventions . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Invariant Content  . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Mail Submission Agents . . . . . . . . . . . . . . . . . . . .  7
   6.  Line Terminaton  . . . . . . . . . . . . . . . . . . . . . . .  7
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