conover(_at_)rahul(_dot_)net (John Conover) writes:
What prompted me to post the question was the high priority assigned
to the Errors-To: header record.
Doing some e-mail header lawyering:
Header precedence sequence as per RFC 822, paragraphs 4.4.2, and
4.4.4, (RFC 2076 discourages use of Errors-To:, used in mailing
lists; From_, which is used as a UUCP header as per RFC 976; Path:,
as per RFC 1036 defined USENET headers; and Return-Receipt-To:, all
of which are non-standard, as per 2076,) Sender: followed by From:,
and Resent-Sender: followed by Resent-From: for the machine
generated address.
If you haven't read the formail manpage since upgrading to 3.14 or later,
you should. The phrase "machine generated" used in previous manpages
doesn't really mean anything at this point. "formail -r" selects the
envelope sender, so in the absence of a Return-Path: or From_, the
headers are examined by the likeliness of them containing the address
of the enveloper sender, though at this point, if you actually get a
message without a Return-Path: then your MTA is broken.
For the trusted address, (i.e., formail -rt,) its similar, with a
header precedence sequence as per RFC 822, paragraphs 4.4.1, and
4.4.4; Reply-To: followed by From:, and Resent-Reply-To: followed by
Resent-From:.
rfc2822 says that Resent-* headers are informational only and should never
be used when generating reply addresses. If you get a message without a
Reply-To:, From:, or Sender:, then falling back to the envelope address
is your best bet.
Or at least that's the theory behind formail's ordering.
Philip Guenther
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