I have seen similar warnings in my mail server log before, but today I did not get the subscribed news circular any more, with the following explanation, for an example:
Nov 27 10:30:50 (EET) sm-mta[51658] (Sendmail): STARTTLS=server, relay=tb-ob0.topicbox.com [64.147.108.117], version=TLSv1.2, verify=NO, cipher=ECDHE-RSA-AES256-GCM-SHA384, bits=256/256
Nov 27 10:30:51 sm-mta[51658]: 4AR8UoZb051658: ruleset=check_mail, arg1=<bounce.mMfed1f3846a9a9e34451d316b.r99b2de7a-1fa6-11ed-9848-270a9134e1fa@xxxxxxxxxxxxxxxxxxxxxxxxx>, relay=tb-ob0.topicbox.com [64.147.108.117], reject=553 5.1.8 <bounce.mMfed1f3846a9a9e34451d316b.r99b2de7a-1fa6-11ed-9848-270a9134e1fa@xxxxxxxxxxxxxxxxxxxxxxxxx>... Domain of sender address bounce.mMfed1f3846a9a9e34451d316b.r99b2de7a-1fa6-11ed-9848-270a9134e1fa@cyrus.bounce.topicbox.com does not existNov 27 10:30:51 sala sm-mta[51658]: 4AR8UoZb051658: from=<bounce.mMfed1f3846a9a9e34451d316b.r99b2de7a-1fa6-11ed-9848-270a9134e1fa@xxxxxxxxxxxxxxxxxxxxxxxxx>, size=11148, class=0, nrcpts=0, proto=ESMTPS, daemon=IPv4, relay=tb-ob0.topicbox.com [64.147.108.1
17]
MTA (Sendmail version 8.18.1) checks the sender's domain (PTR, reverse DNS) to ensure it really exists, if it is not a spammer. I hope there is some way to align the DNS entries of cyrus.topixbox.com
Vladas
