Specified Network Name Is No Longer Available
I just came across a new one in the Exchange 2003 Exchange System Manager. In the Queue Viewer, there is the Additional Queue Information box at the bottom of the screen. This one Exchange server had a lot of messages queued up and most of the queues said: The specified network name is no longer available.
Weirdly enough, on Friday afternoon, this server was chugging along deliverying outbound mail just fine.
A little more investigation showed that DNS name resolution was working fine, too. I tried some telnet tests but the TELNET would never connect to a remote SMTP system.
Turns out that someone had blocked outbound SMTP during the evenings on the WebSense server.