Re: Forwarding problem with aliases

On 05.09.2024 um 17:22 Uhr Knute Johnson wrote:

On 9/5/24 16:10, Marco Moock wrote:

On 04.09.2024 um 14:09 Uhr Knute Johnson wrote:
 

I've got a sendmail server running that needs to forward a couple
of addresses to other destinations.  I've set these up in aliases.
 Most of these work but one recipient has an earthlink account and
it rejects the forwarded message if the sender is not local to the
sendmail server. The error message in the returned mail says "The
sender's address is rejected for policy reasons."  Kind of cryptic.
The end user whitelisted the server's domain but I don't think that
is where the issue is.  I think it is because the sender could be
from anywhere and that doesn't match the domain of our sendmail
server.  But that is just a guess.  If I send mail from an account
on the server to the one of the forwarding aliases, it forwards to
the earthlink account just fine. 

 
If you forward messages, SPF will break. Many sites reject such
messages.
If you now rewrite the MAIL FROM, SPF will be fine but DMARC will
fail if a reject policy is set.
 
You may need to think about implementing ARC with a Milter.
 

 
Thanks for that.  What is ARC?

https://en.wikipedia.org/wiki/Authenticated_Received_Chain

It is a experimental standard that is pushed by the big companies.
It will also help them because they trust big ones, but I dunno how ARC
will be handled that comes from small sites. I assume this will be the
next bullying mechanism.

SPF breaks forwarders, by design.

DMARC is a policy how to handle stuff that doesn't pass DKIM/SPF and
regulates alignment. Some big companies made SPF and DMARC mandatory
which will make forwarders and mailing lists a PITA.

TLDR: In times of SPF and DMARC, forwarding doesn't work like before.
My recommendation: Avoid it whenever possible.

--
kind regards
Marco

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