Advice for Safe Handling of Malformed Messages
draft-ietf-appsawg-malformed-mail-09

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Document Type Active Internet-Draft (appsawg WG)
Last updated 2013-10-29 (latest revision 2013-10-05)
Replaces draft-kucherawy-mta-malformed
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APPSAWG                                                     M. Kucherawy
Internet-Draft                                                G. Shapiro
Intended status: Informational                                  N. Freed
Expires: April 8, 2014                                   October 5, 2013

             Advice for Safe Handling of Malformed Messages
                  draft-ietf-appsawg-malformed-mail-09

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 malformed messages that
   result are non-standard.  Nonetheless, decades of experience has
   shown that handling with some tolerance the malformations that result
   is often an acceptable approach, and is better than rejecting the
   messages outright as nonconformant.  This document includes a
   collection of the best advice available regarding a variety of common
   malformed mail situations, to be used as implementation guidance.

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 April 8, 2014.

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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

Kucherawy, et al.         Expires April 8, 2014                 [Page 1]
Internet-Draft             Safe Mail Handling               October 2013

   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  The Purpose Of This Work . . . . . . . . . . . . . . . . .  3
     1.2.  Not The Purpose Of This Work . . . . . . . . . . . . . . .  4
     1.3.  General Considerations . . . . . . . . . . . . . . . . . .  4
   2.  Document Conventions . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Invariant Content  . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Mail Submission Agents . . . . . . . . . . . . . . . . . . . .  7
   6.  Line Termination . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Header Anomalies . . . . . . . . . . . . . . . . . . . . . . .  8
     7.1.  Converting Obsolete and Invalid Syntaxes . . . . . . . . .  8
       7.1.1.  Host-Address Syntax  . . . . . . . . . . . . . . . . .  8
       7.1.2.  Excessive Angle Brackets . . . . . . . . . . . . . . .  8
       7.1.3.  Unbalanced Angle Brackets  . . . . . . . . . . . . . .  8
       7.1.4.  Unbalanced Parentheses . . . . . . . . . . . . . . . .  9
       7.1.5.  Commas in Address Lists  . . . . . . . . . . . . . . .  9
       7.1.6.  Unbalanced Quotes  . . . . . . . . . . . . . . . . . .  9
       7.1.7.  Naked Local-Parts  . . . . . . . . . . . . . . . . . . 10
     7.2.  Non-Header Lines . . . . . . . . . . . . . . . . . . . . . 10
     7.3.  Unusual Spacing  . . . . . . . . . . . . . . . . . . . . . 12
     7.4.  Header Malformations . . . . . . . . . . . . . . . . . . . 12
     7.5.  Header Field Counts  . . . . . . . . . . . . . . . . . . . 13
       7.5.1.  Repeated Header Fields . . . . . . . . . . . . . . . . 14
       7.5.2.  Missing Header Fields  . . . . . . . . . . . . . . . . 15
       7.5.3.  Return-Path  . . . . . . . . . . . . . . . . . . . . . 16
     7.6.  Missing or Incorrect Charset Information . . . . . . . . . 16
     7.7.  Eight-Bit Data . . . . . . . . . . . . . . . . . . . . . . 17
   8.  MIME Anomalies . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.1.  Missing MIME-Version Field . . . . . . . . . . . . . . . . 18
     8.2.  Faulty Encodings . . . . . . . . . . . . . . . . . . . . . 19
   9.  Body Anomalies . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  Oversized Lines  . . . . . . . . . . . . . . . . . . . . . 19
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