Mail 3.x stopped working

Out of the blue, my mail is not receiving emails anymore.
I deleted .plist, moved the mail folder, you name it I did it.
I am having no problem running entourage so I know my ISP is not blocking my machine.
It must be some application that is preventing mail from connecting to port 110, I just don't know which.
Please help me.

I would still look for corrupt preferences files, as there are some outside of the home folder. Try this app.

And have you tried reinstalling the Mail app?