Hello,
I'm running a postfix mail server on a fresh IP address that has some
bad reputation from the previous owner. So I had a lot of bounces in the
last days which I had to clean up.
One customer complained about a bounce that returned after few days (all
other returned immediately), so I investigated and found the following
issue:
Postfix: connect to the remote MTA
Remote: 220 mx.XXX.YYY ESMTP
Postfix: EHLO mail.XXX.YYY
Remote: 550-REJECT: 49.12.XXX.YYY is in csi.cloudmark.com
Remote: 550 Remediation Portal https://csi.cloudmark.com/en/reset
Remote: (closes connection)
Postfix: HELO mail.XXX.YYY
Postfix: logs "lost connection with ... while performing the HELO
handshake" and defers the message.
So in this case, postfix tries EHLO which fails, then tries to fall back
to HELO (smtp_tls_security_level = may) which hits the closed
connection. The 550 error get lost, so the message is defered, not bounced.
I'm not 100% if that's a BUG or misconfiguration or misbehavior of the
other MTA. But the resulting behavior is at least not what's expected.
Kind regards,
Michael.
