postfix and "username@domain" setup

When using postfix as the mail server, I select "System Settings" --> "Server Templates" --> "Default Settings" and change the "Format for usernames that include domain" to "username@domain".

Creating a new user in a domain creates two entries in /etc/passwd and /etc/shadow

username@domain
AND
username-domain

The major problem happens when you turn on "Vacation" replies in "Usermin". The sender recieves the correct bounce and then a forward error bounce to "username-domain" complaining that a mail loop exists.

Status: 
Closed (fixed)