[Mimedefang] Milter and local Received: line

David F. Skoll dfs at roaringpenguin.com
Sun Mar 4 14:32:11 EST 2007

Philip Prindeville wrote:

> Why is it that when Sendmail passes a message on to the
> Milter, that the local Received: line hasn't been appended
> by that point?

RFC 2821 says:

   When forwarding a message into or out of the Internet environment, a
   gateway MUST prepend a Received: line, but it MUST NOT alter in any
   way a Received: line that is already in the header.

So Sendmail only adds the Received: when it is forwarding the message.
That means it gets added only during local delivery or as part of the
handoff to another SMTP server.

The milter only sees exactly what comes in over the SMTP session.
For Sendmail to synthesize a Received: header at that point would be
more work, and would by lying to the milter about exactly what's coming
in via SMTP.



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