[Dovecot] problems with authentication

Hi, I have some problems

I'm using fetchmail to get my mail from the server to a local server, but the problem is that my user name of the mail is "user@virtualdomain" and I can't make a system user with "@" on centos. So, I want to know how can I tell to dovecot the user "user@virtualdomain" is associate to a sistem user "user.virtualdoman". Or if any one knows another solution.

Thanks Paul

Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com