[Mailman-Users] Mailman causing strange slowdown in SMTP

[Craig Pettersen]

Hi,
  I have a mailman installation running on our qmail server that is involved
in a slowdown in SMTP for the designated SMTPHOST in mm_cfg.py.  I first
noticed that the messages for the list go out very slowly...about 15 seconds
per message.  I saw this in the mailman smtp log, and then I saw it in the
the qmail smtp log as well, so I figured it was a problem with qmail.  As I
looked through the qmail logs, I saw that all messages that connected to
smtp via 127.0.0.1 were slow, averaging more than 15 seconds, while those
that connected from somewhere else were all a fraction of a second.  I
discovered that if I changed SMTPHOST to our public IP in mm_cfg.py, any
messages (from the list or elsewhere) using it would slow down as well, and
any messages connecting via 127.0.0.1 returned to normal speed.  If I shut
down mailman using mailmanctl stop, speed was normal for both localhost or
the public IP, whichever had been used as mailman's SMTPHOST at the time
returning to mormal speed.  That verified that mailman is directly involved
in the slowdown in smtp.  If I telnet to the smtp and manually send a
message, the hangup point is after entering 'data' - ie:

helo test.com
250 ok
mail from: test.com
250 ok
rcpt to: <a valid email>
250 ok
data                      <-------after entering 'data' there is a 15
second + wait if mailman is running
354 ok
etc...



 What could be causing this problem?
This mailman installation serves only one list, an announcement only list,
of about 35,000 members, with over 10,000 disabled due to bounces that send
once every 2 weeks or so. It invariably sends
several hundred to a thousand messages individually at the +/-15sec./message
rate, then a big bulk mailing to most subscribers that's taking about 3000
seconds for around 23,000, then a few score more of individual messages
before it stops functioning.  Using ps aux, one can see that all the
qrunners are there and appear normal, but bin/mailmanctl must be used to
stop and start things to get them going again.
  So my questions are...does anyone have any idea what mailman could be
doing to interfere with smtp on its SMTPHOST and how to fix it? and does
anyone have any idea why mailman stops working shortly after sending out the
big list?

Thanks,
  Craig Pettersen