Mac OS

I have an email account that is no longer valid. When I try to remove it or disable it from Apple's Mail it starts replicating itself very rapidly. When I quit mail and then restart it all those replicated accounts are still there (but it is no longer replicating itself unless I try to disable or remove any of them). If I close Mail and then delete the preferences file and and the Mail folder in ~/Library, then when I start up mail again, it comes up completely clean and just has my mobileme account installed. I can install other accounts no problem, but as soon as I open preferences, the invalid email account is automatically created again, and if I try to remove or disable it it starts replicating again. Does anyone have any idea what is going on and how to fix it?