If you are receiving hundreds (or even thousands) of emails being returned or bounced back to you, you're probably under a Joe Job attack. See: http://en.wikipedia.org/wiki/Joe_job for details.
Basically, the emails are not being sent by you or your account. Someone is using your return email address on email sent from some other email server. There is nothing that can be done to stop it, you just have to ride it out.
Make sure you have your default email address set to :blackhole: as that will help.
