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Re: Mail delivery from Postfix to remote IMAP



On Mon 22 Apr 2024 at 11:20:59 -0700, Greg A. Woods wrote:
> Just keep doing what you're doing.  Anything else _is_ more roundabout.
> Why complicate things?  SMTP forwarding is the way to keep it working!

I agree with you in spirit. Plain forwarding is a basic feature of SMTP.

BUT.

The trouble with plain forwarding is that my mail server's domain name
doesn't match the domain name in the From: header, and doesn't match the
envelope FROM domain, and it doesn't match the SPF policy of the sender
domain etc etc. Those are things that are checked by DKIM/DMARC/SPF.

And you can't change the From: header because that is changing the mail
(and invalidates the DKIM signature), and neither can you change the
envelope FROM address because bounces (as far as they happen) won't work.

> Of course fixing your mail server to do proper DKIM, or even just
> futzing with SPF (and PTR) records enough to get normal SMTP port#25
> through, i.e. without heavier AUTH and use of the submission service,
> would be even simpler.  I've done the latter, and hope to do more with
> DKIM soon (but _NOT_ with the milter mess!).

Unfortunately DKIM is designed to break forwarding... I can't think of a
way to change an email message to make it DKIM-compliant. Mailing lists
can get away with changing the From: header to something like
"list%example.org@localhost (Rhialto via Example-List)" (and that's already an
ugly thing to do) but that's not an option for individual mails.

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert                            <rhialto/at/falu.nl>
\X/ There is no AI. There is just someone else's work.           --I. Rose

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