Advice for Safe Handling of Malformed Messages
draft-ietf-appsawg-malformed-mail-02

The information below is for an old version of the document
Document Type Active Internet-Draft (appsawg WG)
Last updated 2012-06-27 (latest revision 2012-05-19)
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 AD is watching
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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                                           Cloudmark, Inc.
Intended status: Informational                              May 19, 2012
Expires: November 20, 2012

             Advice for Safe Handling of Malformed Messages
                  draft-ietf-appsawg-malformed-mail-02

Abstract

   The email ecosystem has long had a very permissive set of common
   processing rules in place, despite increasingly rigid standards
   governing its components, ostensibly to improve the user experience.
   The handling of these come at some cost, and various components are
   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.

   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.  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 simply reject
   or discard them.  Accordingly, this document presents recommendations
   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

   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."

Kucherawy               Expires November 20, 2012               [Page 1]
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   This Internet-Draft will expire on November 20, 2012.

Copyright Notice

   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.

Kucherawy               Expires November 20, 2012               [Page 2]
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  The Purpose Of This Work . . . . . . . . . . . . . . . . .  4
     1.2.  Not The Purpose Of This Work . . . . . . . . . . . . . . .  4
   2.  Document Conventions . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Key Words  . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Internal Representations . . . . . . . . . . . . . . . . . . .  5
   5.  Invariate Content  . . . . . . . . . . . . . . . . . . . . . .  5
   6.  Mail Submission Agents . . . . . . . . . . . . . . . . . . . .  6
   7.  Line Terminaton  . . . . . . . . . . . . . . . . . . . . . . .  6
   8.  Header Anomalies . . . . . . . . . . . . . . . . . . . . . . .  7
     8.1.  Converting Obsolete and Invalid Syntaxes . . . . . . . . .  7
       8.1.1.  Host-Address Syntax  . . . . . . . . . . . . . . . . .  7
       8.1.2.  Excessive Angle Brackets . . . . . . . . . . . . . . .  7
       8.1.3.  Unbalanced Angle Brackets  . . . . . . . . . . . . . .  8
       8.1.4.  Unbalanced Parentheses . . . . . . . . . . . . . . . .  8
       8.1.5.  Unbalanced Quotes  . . . . . . . . . . . . . . . . . .  8
     8.2.  Non-Header Lines . . . . . . . . . . . . . . . . . . . . .  8
     8.3.  Unusual Spacing  . . . . . . . . . . . . . . . . . . . . . 10
     8.4.  Header Malformations . . . . . . . . . . . . . . . . . . . 10
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