[Mailman-Users] Non-Delivery of Mail

[David Andrews]

I run a cPanel system that, among other things, supports about 300 
Mailman lists. We have about 20,000 users. I am getting lots of 
bounced messages from roadrunner.com and various XXX.rr.com domains. 
It looks like they may be blocking my domain nfbnet.org although I am 
not sure how you tell.

When I look at a mail delivery report via cPanel, I see messages that 
say 421 too many concurrent connections, connection refused.  What 
can I change to fix this problem!

Thanks!