Simple solution is to configure the server to not send any DSNs for forwards
at all.
Since DSNs do have a blank sender, a trick is to have a router which detects
a blank sender, and if receiver of the bounce isn't someone on the same
domain, then blackholes it. (use :blackhole: as redirect data)
-----Ursprungligt meddelande-----
Från: Yves Goergen via Exim-users <exim-users@???>
Skickat: den 23 december 2020 20:34
Till: List: exim <exim-users@???>
Ämne: [exim] Forward from external immediately without queue
Hello,
I noticed in my log files that I have situations where some mail is received
from externally which is supposed to be forwarded to externally (with the
'redirect' driver, or 'remote_smtp' transport?). Now if my spam filter
didn't detect the message but it was rejected by the forward recipient, Exim
will generate a bounce message and try to send it to an arbitrary sender
which is mostly fake. This is causing backscatter, which may cause issues
with my mail server reputation in general. (I know that the RFC requires
that behaviour, but that RFC is broken and not practical, for well-known
reasons.) The same probably happens when the remote mailbox is full.
I tried to understand what the 'errors_to' directive does but it's hard to
follow those descriptions. So I'm not sure whether it's useful in my case.
So I had another idea. If queuing and bouncing is the problem, can I get rid
of that? If a message comes in from an unauthenticated sender, that must be
another mail server. Those have got time, there's nobody waiting in front of
a screen for the message to be submitted. So could Exim just try to deliver
the message immediately in this case? If that fails, it could directly
reject the message in the waiting original connection. No need for bounces.
If the remote error is permanent, so should be Exim's. Same for temporary
errors. Passing back the remote error message is probably a privacy concern
as it might disclose the forward address or provider.
This must only apply to forwards for unauthenticated senders.
Authenticated senders are my users, they provided a password and I know I
can send them bounces safely. And they're waiting for completion of the
submission.
How would a configuration of this look like? Or where in the documentation
can I find more information about that?
-Yves
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