We are using ListServ 15.5 and are relaying out to a group of 5 smtp server at our enterprise level.  The logs on these servers are filled with:

09-13-2010.00:10:04 SMTPserver-522: 1963484 host connection threshold exceeded for xxx.xxx.xxxxx.xx.xx
09-13-2010.00:10:04 SMTPserver-522: 1963485 host connection threshold exceeded for xxx.xxx.xxxxx.xx.xx
09-13-2010.00:10:05 SMTPserver-522: 1963486 host connection threshold exceeded for xxx.xxx.xxxxx.xx.xx

the logs on our side look like:

14 Jun 2010 09:26:08 <421 Service not available, closing transmission channel

like 400,000 times a day.

The Listserv logs look normal.  All the list are working fine.  

Has anyone  run into this before?

Thanks in advance,

Rick