We are having issues with our maling list, we are using MailMan, a piece of log that i thought it might help in tracking the issue,
Multiple lines like the following:
(lost connection with mx1.hotmail.com[65.54.188.110] while sending MAIL FROM
Then at the end the following is received:
(host mx1.hotmail.com[65.55.92.136] said: 550 SC-002 (SNT0-MC1-F20)
Checking that error message means:
SNT0-MC1-F20
Mail rejected by Outlook for policy reasons. The mail server IP connecting
to Outlook has exhibited namespace mining behavior.
I have tried to check if there is something wrong with our dns record, one thing i have noticed is that:
mail.example.com is a CNAME to example.com and example.com
is an A record to server ip.
I have mentioned here hotmail as an example of the servers we are trying to connect, some of these servers succeed, unfortunately most of them fails [i guess the ones that checks well before the receiving an email.]
Please suggest any idea that you might thing could be the cause, Could be the DNS record issue i mentioned be the cause? Also please note that we already have a PTR rescod for the mail server IP.
Other logs:
Dec 18 10:15:44 mail postfix/smtp[688]: D9FC3E000E0: to=<info@example.org>, relay=none,
delay=319639, delays=319597/0.28/42/0, dsn=4.4.1, status=deferred (connect to
mailbk.example.org[x.x.x.x]:25: Connection timed out)
Dec 18 10:15:44 mail postfix/error[846]: 87571E000D7: to=<info@example.org>,
relay=none, delay=332315, delays=332272/43/0/0.13, dsn=4.4.1, status=deferred
(delivery temporarily suspended: connect to mailbk.example.org[x.x.x.x]:25:
Connection timed out)