I had this problem crop up and I thought it was a fatal error on the server. There were other problems like the GUI going out of whack and ftp not working properly.

I restored the whole server and tested it but I'm still not getting any email in. The mail box is always unavailable. Some of the mail goes missing completely, doesn't even get returned to the sender.

Having spent most of the night restoring and testing I can't think why this is still causing a problem?

The server is behind a firewall, if this was improperly configured would that cause this sort of problem?

Cheers, Rob.