[Mailman-Users] Mailman server consuming entire Internet pipe (dual T1)

[Scott Race]

Hello,

Starting Friday this particular office started having massive Internet trouble (dual T1s). Running a speedtest shows 2.75Mbps download (fine) and about .09Mbps upload (not fine).  There are about 15 active lists on this server, a few of the lists have a few thousand members.

We traced the network issues to our mailman server.  With Mailman server turned off, network is fine.  As soon as it comes back up, bandwidth consumed.

Using Postfix as the MTA, set the default_process_limit to 3 in the master.cf file.  Other settings are postfix defaults (main.cf)

Haven't been able to figure out exactly what's up - but I do know if I set an iptables rule to block all inbound port 25 traffic, issues go away - so...

I've done some basic testing for open relays, so far I have not found anything indicating it's an open relay. Packet sniffing shows connections from a number of IP addresses to the Mailman server.  Outside test shows the hostname is not an open relay, and I can't telnet on port 25 with standard HELO command.  All internal mail comes to a Barrucuda spam filter unit.

/usr/local/mailman/logs/post shows 19 posts today to the various lists.

from my main.cf:

mynetworks = 172.10.0.0/16, 127.0.0.0/8
#relay_domains = $mydestination
mydestination = $myhostname, $mydomain, localhost
myhostname = lists.lists.mydomain.com
mydomain = lists.mydomain.com


At this point I can't tell if I have a Postfix problem or Mailman problem. Any ideas?  Thanks!!

Scott