Advice for Safe Handling of Malformed Messages
RFC 7103
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Type |
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RFC - Informational
(January 2014; No errata)
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Last updated |
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2015-10-14
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Replaces |
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draft-kucherawy-mta-malformed
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IETF
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plain text
pdf
html
bibtex
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WG state
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Submitted to IESG for Publication
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Document shepherd |
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Moonesamy S
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Shepherd write-up |
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Show
(last changed 2013-09-28)
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| IESG |
IESG state |
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RFC 7103 (Informational)
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Consensus Boilerplate |
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Yes
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Telechat date |
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Responsible AD |
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Barry Leiba
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Send notices to |
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(None)
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| IANA |
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Version Changed - Review Needed
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No IANA Actions
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Internet Engineering Task Force (IETF) M. Kucherawy
Request for Comments: 7103 G. Shapiro
Category: Informational N. Freed
ISSN: 2070-1721 January 2014
Advice for Safe Handling of Malformed Messages
Abstract
Although Internet message formats have been precisely defined since
the 1970s, authoring and handling software often shows only mild
conformance to the specifications. The malformed messages that
result are non-standard. Nonetheless, decades of experience have
shown that using some tolerance in the handling of 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; it is to be used as
implementation guidance.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7103.
Kucherawy, et al. Informational [Page 1]
RFC 7103 Safe Mail Handling January 2014
Copyright Notice
Copyright (c) 2014 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, et al. Informational [Page 2]
RFC 7103 Safe Mail Handling January 2014
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 . . . . . . . . . . . . . . . . . . . . . . 5
5. Mail Submission Agents . . . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . . . . 10
7.1.7. Naked Local-Parts . . . . . . . . . . . . . . . . . . 10
7.2. Non-Header Lines . . . . . . . . . . . . . . . . . . . . 10
7.3. Unusual Spacing . . . . . . . . . . . . . . . . . . . . . 12
7.4. Header Malformations . . . . . . . . . . . . . . . . . . 13
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 . . . . . . . . . . . . . . . . . . . . . 18
8. MIME Anomalies . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Missing MIME-Version Field . . . . . . . . . . . . . . . 19
8.2. Faulty Encodings . . . . . . . . . . . . . . . . . . . . 19
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