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From: Knute Johnson <knute2024@585ranch.com>
Newsgroups: comp.mail.sendmail
Subject: Re: Forwarding problem with aliases
Date: Fri, 6 Sep 2024 08:24:39 -0500
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On 9/6/24 03:59, Marco Moock wrote:
> 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.
> 

Thanks Marco.

-- 

Knute Johnson