From time to time it seems the IIS 6 SMTP service will just stop relaying mail. It will continue to accept it, causing a queue to build up, but it won't send it out the other side. We have GFI MailEssentials 12 (latest build) installed on the server along with GFI MailSecurity. The server is configured with each of the domains to accept and relay them to a smart host (host name is correct, resolves fine, and is in the internal network). When we experience the problem it seems a simple IISRESET does the trick and mail starts flowing again and the queue is reduced to the average amount.
What is annoying about this is that we have had to bring in a third party service, Maillive!, to send test messages through the system every ten minutes to monitor it. For all intensive purposes SMTP is up and running according to the Service Control Manager, and it is accepting email from the outside. When it stops sending though the queue backs up very quickly (we receive about 1M messages/week). If all else fails we'll take hang dumps and send them to PSS, but I'd like to see if the community is aware of anything first before we go towards that next step. Is there tracing or some other logging that we can turn up to see what is happening with SMTP at that moment?
I just saw SMTPDiag and will give that a shot the next time it occurs, but if there is any other tips and tricks I would appreciate it!
Thanks,
Colin