Hi > This can happen when receiving mail takes more time - your server reports > mail as accepted but the sending server notices a delay and considers > attempt unsuccessful.
Indeed, this was my first suspect the milter which runs the longest is, after 'DATA END' MIMEDefang (running SpamAssassin / ClamAV) as engaged as part of the decision taking if that email shall be accepted or rejected. This usually takes less than 10 seconds, in high load situations up to a minute or more. https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.3.2.6 There is plenty of time to do so! Postfix default config has a timeout of 5 Minutes. So if the milter takes too long, postfix would report TEMPFAIL and no duplication would occur. At leas, this is how I observed the situation in the past if loads get too high to handle timely. > Doesn't scanning of mail too much time when receiving mail from outlook.com? Unless the sender does not obey RFC timeouts, this should not be the issue. I am investigating in a different direction now. I have added quite some logging of all filter stages in MIMEDefang. They return as expected timing looks right. But further digging hints to an issue with the OpenDMARC Filter. During investigation I noticed a very large number of open TCP connections to our DNS server. Of course, if a large reply is expected, the resolver prefers TCP over UDP. Sadly, OpenDMARC in log very logging friendly. I fear our DNS server could have rate limited TCP DNS requests leading to OpenDMARC taking way too much time to return. Also, it's not as I first concluded, an issue only affecting sender behind outlook.com. I also have found other domains, not on the Microsoft cloud, most probably being affected. I guess the email reading client is also somehow involved. If it performs de-duplication by Message ID, the customer never notices. Mit freundlichen Grüssen -Benoît Panizzon- -- I m p r o W a r e A G - Leiter Commerce Kunden ______________________________________________________ Zurlindenstrasse 29 Tel +41 61 826 93 00 CH-4133 Pratteln Fax +41 61 826 93 01 Schweiz Web http://www.imp.ch ______________________________________________________ _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
