Dear Lazyweb: Backing up Email in Evolution

Dear Lazyweb,

My university generously provides us with a whopping 25 megabytes of email storage, and has been sending me messages on a daily basis that my inbox is 93% full.

I use Evolution as my mail client, and it's an IMAP mail server.
How can I download my 23 megs of emails and a stick them in a tarball?

If anyone has any ideas or hints on this, I'd appreciate it very much if you dropped me a comment. :)

Thanks!