I think this problem is from your enterprise SMTP servers.  They're objecting to Listserv sending too many messages in one connection.  You'll need to contact whomever runs those servers and ask them to "whitelist" your Listserv server.

Melissa

________________________________________
From: LISTSERV site administrators' forum [[log in to unmask]] On Behalf Of Rick Scheller [[log in to unmask]]
Sent: Monday, September 13, 2010 11:08 AM
To: [log in to unmask]
Subject: [LSTSRV-L] host connection threshold exceeded for...

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