How do we prevent the mail.box file from becoming corrupted?

We have Domino R5.0.11 on Windows 2000 server and Norton Antivirus Corporate Edition 7.01. For the last few days, we have seen a problem that the mail.box file is corrupt: "SMTP Server: Error opening mail box: Database is corrupt -- Cannot allocate space."

We already know how to fix this problem, but we don't know how to prevent it.
It could be a number of things, but NAV Corporate is not NAV for Domino. NAV cannot scan Domino files on the fly. Only NAV for Domino can. I would start by excluding your Domino directory from being scanned. If that cures your issue, look into buying NAV for Domino. If you are still getting corruptions, you will need to look elsewhere, such as malformed headers in messages.