Mail anyone helP???

I have mobile me set up with my iphone and mac. Everything worked great up until an hour ago. All of the sudden my college email address @umich.edu is not working. I tried to compose an email from it and it goes straight to outbox saying sender email is invalid. I deleted the account off of apple mail and my phone and reinstalled and it still does it. I can receive email sent to it but when i go to send it says sender email invalid. Anyone know why this might be?

 

working..kinda

WEll now I am able to send emails, but it sends two copies...What is going on?