I concur with Melissa. It's likely a remote email host is complaining that you sent them too many messages (or in my case a message with too many recipients) to that site. I tried to appeal to the remote email administrator without success--"they didn't have a problem". I finally reconfigured my email server so that outbound messages to that site were broken down into 5 recipients per message copy. That was the solution to my problem - your mileage may vary. -Rich > -----Original Message----- > From: LISTSERV site administrators' forum [mailto:LSTSRV- > [log in to unmask]] On Behalf Of Kenny, Melissa S > Sent: Monday, September 13, 2010 12:34 PM > To: [log in to unmask] > Subject: Re: host connection threshold exceeded for... > > 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