Ah. Then you can't. Thunderbird doesn't filter mail by address. There are huge lists out there containing known spam-domains, though, but as so much junk email these days fake most of the headers anyway this type of content filtering is very inefficient unless done on the server-, or even the ISP level.
Your university may be already be applying server-side content control, even if there are no explicit filtering done for your account. If so there are could be a custom header field inserted to the messages that you could use for client-side filtering. Ask your IT department.
Edit: If you're using Thunderbird at home to access the same account as you're using with the webmail interface I guess you could set up Thunderbird to purge messages from the server when you delete them from your inbox locally. Unless the server is IMAP this can prove impractical, though, if you wish to maintain consistency with the online access while still organizing mail in folders locally.