[Mailman-Users] Message-ID required

Stephen J. Turnbull turnbull.stephen.fw at u.tsukuba.ac.jp
Tue Feb 6 05:05:28 EST 2018

Mark Sapiro writes:
 > On 02/05/2018 12:22 AM, Stephen J. Turnbull wrote:
 > > 
 > > According to RFC, Message-ID is an originator field, and MUST be
 > > present and MUST be unique.
 > Do you have a reference for this? I thought this was correct, but I
 > recently looked it up in RFC 5322 and predecessors and those RFCs
 > at least say it's optional and SHOULD be present.

You're right.  I knew that it was SHOULD in RFC 822, but I thought
this was updated in RFC 1123 "Host Requirements" or maybe RFC 5598
"Email Architecture".  I was wrong.

In any case, SHOULD is pretty close to MUST, especially in this case.
(What reasons based on interoperability issues can you think of for
omitting Message-ID?  SHOULD means you need one!)

I'm guessing that since the RFC authors have deprecated use of
Message-ID for anything related to security, and its semantics are a
judgment call in any case, it's simply not reliable enough to promote
to MUST.  So they never did.


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