Author: Jeremy Harris Date: To: exim-users Subject: Re: [exim] Retry rule of NDR based on error
On 10/05/14 04:14, Thomas Hommers wrote: > my exim server acts as gateway, some email is rejected as spam by the destination server and exim therefore creates a NDS (bounce) message.
> Because a lot of the spam senders won't send with a legit sender address, exim continues trying to send the NDR even tough the destination rejects the email or the recipient does not exist. [....] > How could i achieve this or maybe there is another much easier way?
Bounces, and backscatter, and undeliverable bounces,
are inherent in a setup like yours where a store-and-forward
system forwards to another system which can reject.
If the second system only rejects at RCPT time, exim as the
first system can be set up to do recipient callout verification.
This permits the rejection from the second system to
cause rejection from the first, during the original SMTP
conversation with the source. Thus the message is never
accepted by exim and no bounce need be created.
If the second system can also reject at DATA time
(eg. because it does content scanning)
exim can be set up to do cutthrough routing. Here
it delivers (most) messages to the second system
while receiving them from the source - and does
not signal acceptance to the source until acceptance
is received from the second system. Again there
is no need to create a bounce for the cases where
the second system rejects the mail.
[ You can't do anything about the second system
itself creating bounces, but we're not dealing with
that here. ]
What cutthrough routing does is to take out the
store-and-forward aspect of MTA operations.
Recipient verify callouts are a halfway house.
