[apps-discuss] I-D Action: draft-ietf-appsawg-malformed-mail-04.txt

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Subject: [apps-discuss] I-D Action: draft-ietf-appsawg-malformed-mail-04.txt
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A New Internet-Draft is available from the on-line Internet-Drafts directories.
 This draft is a work item of the Applications Area Working Group Working Group of the IETF.

	Title           : Advice for Safe Handling of Malformed Messages
	Author(s)       : Murray S. Kucherawy
                          Gregory N. Shapiro
	Filename        : draft-ietf-appsawg-malformed-mail-04.txt
	Pages           : 19
	Date            : 2013-05-17

   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

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