Paul van der Vlis via Postfix-users:
> Hallo,
>
> Unfortunately, I have quite a few customers who want to receive email
> from their own domain at a different email address, such as a Gmail or
> Hotmail address. I forward this in /etc/postfix/virtual.
>
> But I actually don't understand why this arrives, especially if the
> sender has an SPF or DMARC clearly states that it should be rejected if
> the email comes from the wrong IP.
If a message has valid DKIM signatures (the message header and body
still match) and the receiving systemn verifies DKIM, then it may
still accept forwarded mail, despite SPF mismatch.
> Perhaps Gmail and others don't care about that, but it could also be
> that they look beyond the forward address and see that it comes from a
> legitimate IP, but only forwarded is.
> That would be good, but maybe easily forged without DKIM?
>
> Could someone tell us more about this?
>
> And what is a good solution for forwarding? Rewrite the sender? SRS?
If the receiving system insists on SPF despite valid DKIM, yes. I have no
first-hand experience doing that, but there is some SPF and SRS tooling.
This is a part of Postfix that needs some work.
Wietse
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