Yeah, no offense to Roger, but that wasn't a very good suggestion, especially since we knew you were dealing with MobileMe. Most - not all, but most - SMTP (outgoing) servers will adamantly refuse to send e-mail having a From address that doesn't match the address of their service, as a measure to protect them against abuses by spammers. MobileMe is one of those. So, if you have an e-mail address like coyote@someuniversity.edu, and you try to use the smtp.me.com server to send mail from that address, it will refuse. The smtp.me.com server will only send mail from addresses ending in @me.com.
What this means, unfortunately, is that there really
isn't a way to do what you're asking, unless you have another account on a server that will allow this sort of thing. If you want to send mail from your university address, you'll have to send it using the university servers.