Hi Exim Users!
There were two problems. First the defer_ok Flag should be used twice as
Lena mentioned.
verify = recipient/defer_ok/callout=10s,defer_ok,use_sender
Second the callout timeout was 2m and therefore to long for the
SMTP-Clients which run into SMTP/TCP-timeout
before completing the Callout.
Additionally the target system has (maybe intentional) one dysfunctional
(time at each connect) mailserver prioritized above the others. Maybe
this is to scare away SPAMMERS. Nevertheless it contributes to the
problem negatively.
IMHO all such dirty hacks to prevent SPAM makes it really hard for other
admins to have their mailsystems run smoothly and should be avoided. We
run two large Email-Servers and never had the need for such tricks. Our
SPAM suppression rates are fairly high 99% of incoming E-Mail is
filtered out. And the rate of false positives is one Email per month and
our customers can deal with that utilizing their individual whitelists
on customer and domain and email address level.
Many thanks to all here contributing to the solution of this nasty problem.
Cheers
Volker
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inqbus Scientific Computing Dr. Volker Jaenisch
Richard-Strauss-Straße 1 +49(08861) 690 474 0
86956 Schongau-West http://www.inqbus.de
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