On Mon, 10 Nov 2003, Phil Pennock wrote:
> Is there a particular reason why Exim always fixes up the Resent-
> headers, including adding new headers?
RFC822 and RFC2822 specify that certain header lines must be present.
Exim makes sure this is the case. IIRC, it is still working to 822,
which insists on more lines than 2822.
2822 requires Date: and From: whereas 822 also requires either To: or
Cc: or Bcc: (again, IIRC).
And they both require Message-ID, though 2822 has this as a SHOULD
rather than a MUST.
As for resent- headers, RFC 2822 has this to say:
When resent fields are used, the "Resent-From:" and "Resent-Date:"
fields MUST be sent. The "Resent-Message-ID:" field SHOULD be sent.
"Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be
identical to "Resent-From:".
If any Resent- header exists, Exim makes sure there is a complete set,
as for the non-Resent- headers.
> I can see it making sense for initial submission, or as a default for
> relay_from_hosts,
Exim has no built-in concept of "initial submission" or "relay
submission".
> issues at the moment getting a good set of test-cases to figure out when
> Exim changes which set of Resent- headers, when there are multiple
> Resent- sets of varying quality.
Multiple Resent- sets (as discussed on a thread some time ago) are a
total disaster for a number of reasons, not least of which is that there
is no seriously enforced ordering of header lines. That is why many
mail-processing programs (MUAs and MTAs) amalgamate multiple Resent-
sets or rename old ones to X-Resent-xxx when adding new sets.
Philip
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
Get the Exim 4 book: http://www.uit.co.uk/exim-book
