To delete emails on the server, wouldn't you have to configure the server itself? Unless the host has some program that lets you set local config files of some sort. No idea. Maybe you should email the hosts and tell them to start filtering things on their side, since it is costing them tons of bandwidth too to keep sending viruses all over the place.

One thing I used to do is set a spam filter rule in whatever client I happened to be using that auto-deleted all emails over a certain size, say 100k, since anything that big was likely to be a virus. If you can set up a rule to auto-delete all files with attachments of a certain kind that'd be better. Does norton scan emails right after they download, or right after they're saved into a folder somewhere? If it scans as they download, before they're even written to disk, then that won't work, I guess.

Another solution I had to resort to for the email from my FF1 site for a while (due to viruses) is using webmail. They have a webmail interface, which does give you access to the emails while they're still on the server, so you can hand-delete the emails without downloading them. If they have webmail and it's sophisticated enough, maybe you can even set a spam filter in there.

Sorry for the customary linux babble, but right now I run fetchmail as a cron job every 5 minutes, which pipes to procmail, which pipes to spamassassin, and then I can auto-forward spam to /dev/null or ~/.maildir/spam or wherever I want. Handling a few emails every 5 minutes is better than 400 emails all at once. Any way you could have your computer fetch and filter emails constantly like that?