On Wed, 1 May 2024, Jeremy Harris via Exim-users wrote:
On 01/05/2024 22:42, The Doctor via Exim-users wrote:
What is external forwarding?
Sound like something scary.
My *guess* is:
You mailed person A.
... or someone pretending to be you mailed A ...
A has their mails configured, at the MX for A,
to be forwarded to B. You don't have control over that
configuration;
it is entirely A's choice. He wanted it to be done.
But you have configured your system, probably in "SPF" terms,
you
say "any messages claiming to be from me *must* be be sent by
*my* system.
Any messages being sent by any other system are invalid, and
should be rejected."
The message is being sent onwards by A's MX to B's MX. it is
being sent by
A's MX, as far as B's MX is concerned.
B's MX implements SPF, and does what you claim you wanted. It
rejects the
message, since the message did not arrive at that host directly
from your MX.
And thus, a traditional and useful feature of email handling
has been broken.
--
Cheers,
Jeremy
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