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[18.104.22.168] while sending MAIL FROM
Then at the end the following is received:
(host mx1.hotmail.com[22.214.171.124] 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.
Dec 18 10:15:44 mail postfix/smtp: D9FC3E000E0: to=<email@example.com>, 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: 87571E000D7: to=<firstname.lastname@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)