We have an Exchange 2010 Server SP1 which is running the Hub Transport, Client Access and Mailbox Server roles all on one physical box.
The issue we encountered the other day is that ALL mail flow effectivly stopped and we have over 1000 messages sitting in the Mail Submission Queue. This meant that even internal mail being routed had stopped and was polling in this queue.
We first tried restarting Exchange Services such as the Information Store and Transport service. This did not work and mail was still polling and increasing in the Mail Submission Queue.
I then read somewhere that it could be caused by IIS so I performed an iisreset to restart the IIS services.
After IIS came back online sure enough the Mail Submission Queue started dropping and all mail started flowing again and delivering to mailboxes.
We run on the Exchange Server the built in anti-spam agents and Symantec EndPoint Protection Anti-Virus only. We have Messagelabs that scan our external mail for spam before delivering to the mail server.
So my question is.... Why is that restarting IIS caused the Mail Submission Queue to start processing normally? I am very concerned about this and would like some guidance on what the issue could be...
Thanks in advance.