Cowbay via Postfix-users:
> Hello,
>
> My Postfix is 3.4.23-0+deb10u2. It's old.
>
> I got a rare mail with the Resent-Sender header and no other Resent- headers.
>
> Since I configured the local_header_rewrite_clients, cleanup(8) insert the
> missing Resent- headers for this mail.
>
> According to RFC 5322 Appendix A.3.
> (https://datatracker.ietf.org/doc/html/rfc5322#appendix-A.3)
>
> resent fields are prepended to the message:
> ----
> Resent-From: Mary Smith <m...@example.net>
> Resent-To: Jane Brown <j-brown@other.example>
> Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800
> Resent-Message-ID: <78...@example.net>
> From: John Doe <jdoe@machine.example>
> To: Mary Smith <m...@example.net>
> Subject: Saying Hello
> Date: Fri, 21 Nov 1997 09:55:06 -0600
> Message-ID: <1234@local.machine.example>
>
> This is a message just to say hello.
> So, "Hello".
> ----
>
> However cleanup(8) didn't prepend but append. It's like below:
> ----
> From: John Doe <jdoe@machine.example>
> To: Mary Smith <m...@example.net>
> Subject: Saying Hello
> Date: Fri, 21 Nov 1997 09:55:06 -0600
> Message-ID: <1234@local.machine.example>
> Resent-From: Mary Smith <m...@example.net>
> Resent-To: Jane Brown <j-brown@other.example>
> Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800
> Resent-Message-ID: <78...@example.net>
>
> This is a message just to say hello.
> So, "Hello".
> ----
>
>
> There is another interesting behavior that if there is no Message-Id
> header, cleanup(8) won't insert the Message-Id header and append
> all missing Resent- headers.
Postfix adds a missing (Resent) Message-ID, Date, or From header
when a message is received as an original or resent submission, not
when it receives a message from a remote MTA (for some definition
of 'remote').
(Postfix detects that a message is resent when it contains a Resent-
header, including Resent-From, Resent-Message-Id, Resent-To,
Resent-Cc, Resent-Bcc, Resent-Reply-To, or Resent-Sender).
The Postfix Resent- implementation is based on RFC 822 which in
section 4.1 syntax appears to suggest that 'originator' (From:,
Sender:) come before before 'resent' (Resent-From:, Resent-Sender).
Also, in RFC 822 the interpretation of multiple "Resent-" fields
of the same type was explicitly undefined. There were no multiple
Resent- blocks, let alone whether a newer Resent- block precedes
or follows an older one.
Thus, the Postfix implementation supports one Resent- block, and
its placement meets RFC 822 requirements.
(The implementation was done at a time that prepending would have
been technically impossible, because Postfix reads and writes out
headers one by one, and it would not have been able to prepend
something to a header that it had already written out.)
So yeah, you can blame me for not parsing RFC 5322 for changes
in Resent handling.
Wietse
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