Best Current Practices for Handling of Malformed Messages

The information below is for an old version of the document
Document Type Expired Internet-Draft (appsawg WG)
Last updated 2011-08-12 (latest revision 2011-07-26)
Replaces draft-kucherawy-mta-malformed
Stream IETF
Intended RFC status Best Current Practice
Expired & archived
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Stream WG state WG Document
Document shepherd Jiankang Yao
IESG IESG state Expired
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Responsible AD Pete Resnick
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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 memo includes a collection of the best current practices in a variety of such situations, to be used as implementation guidance. It must be emphasized, however, that the intent of this memo is not to standardize malformations or otherwise encourage their proliferation. The messages that are the subject of this memo 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 memo 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.


Murray Kucherawy (

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