Thunderbird should be able to send.

Thunderbird should be able to recieve.

Your machine should not send to recieve mail over 1 million bytes.

You should have a working .forward file.

All mail destined for "abuse" should really go to 'root'.  There should be no account named 'abuse'.

A copy of all mail destined for your account @nmu.edu should go to your account on your machine.  Remember that NMU will not forward email.

You should send an undeliverable piece of mail and see what happens. (I.e. mailto: fred@doesnotexist.com)

You should try and send mail with the ethernet cable disconnected.  See what happens.  What happens when you plug it back in?