I have a Mac Mini, and I am having some problems with the mail application.

I can't receive any emails, and I'm having problems sending them. I get a spinning wheel beside the 'sent' folder like it trying to send the last email, and it puts a copy of the email into the 'outbox'.

Mail thinks the email isn't sending, but it has sent the email, and continues to send it over and over.

I have deleted the email out of the outbox, as well as stopping mail from sending the current email, but everytime I re-open mail it starts the process over again...

Does anyone know what this problem could be, and how I fix it?