Creating FTP and Mail users for Virtual Servers

I have Virtualmin running on Fedora Core 7 and having the following issue.
When I create a user "john" for a virtual server the username is as follow:
jonh.domainname

I’m trying to find out what I need to edit so the .domainname does not get append to the username.

Module Configuration->Defaults for new domains->Include domain name in usernames? "Only to avoid a clash"

Module Configuration->Defaults for new domains->Include domain name in usernames? "Only to avoid a clash"
not work again if
we have or cusotomer have another domain and create the same name email.
example : if we have domain name jhon.com, and we make email name jhon,then we email is jhon@jhon.com and in same virtualmin server
then another customer have domain joe@com, and make email with name john, then he email not john@joe.com but john.joe.com@joe.com not john@joe.com … like it is virtualmin another bug…