[Mailman] Problems with receiving emails from mail.python.org

[Tomas Brandysky]

Hello,

we have encountered some problems with receiving emails from python-dev
mailing list.

The problem started when some of our employees being subscribed to
python-dev mailing list were unsubscribed from the list with the message
saying that too many emails were bounced.

We were checking the logs to look for bounces as we were sure we had no
problems with our mail server by that time. We really found out there
were no bounces at all in logs but we could see few strange errors when
receiving emails from mail.python.org:

timeout after DATA from mail.python.org[82.94.164.166]

We've discovered the source of the problem was in Cisco ASA 5520 box
with SMTP inspection enabled. The main purpose of this box is to look
into traffic and once the traffic seems to be not legal or not RFC
compliant it drops the connection for security reasons.

Since we disabled the SMTP inspection all emails from python-dev mailing
list were received without problems.

We think the problem could be on mail.python.org server setup as we are
receiving thousands of emails every day and almost none of them have
such a problem.

Not all emails coming from mail.python.org are dropped but it's still a
large portion which leads your server think the messages are bounced and
users are unsubscribed from the list then.

Could you please verify the configuration of your mail server to be sure
the problem is not on your side. Otherwise this would be a problem of
Cisco box but strange thing is that this behaviour is seen only on
incoming traffic from mail.python.org.

Thank you very much
If I can help you any further please let me know

Best regards

Tomas Brandysky
System Administrator
I3 CZ s.r.o.

tel: +420 227 031 252
GSM: +420 602 150 316