adding new mail user creates two accounts!?!

Hi.

I've installed VirtualMin and am trying to get my head around the whole thing.

I am wanting users to be able to log into their email accounts using:

username@mydomain.com

I changed the settings in:

"Virtualmin Virtual Servers > Server Templates > Default Settings > Mail for Domain"

so that "Format for usernames that include domain" is set to "username@domain".

Now when i add a new email user - it creates two email accounts (as seen in readmail):

"username@mydomain.com" AND "username-mydomain.com"

both of these accounts can be logged into via POP3

however - when an email is sent to "username@mydomain.com" it gets sent to the "username-mydomain.com" mailbox.

How can I change it so that only the "username@mydomain.com" is set up when a new email user is added - and the mail is delivered to that user?

I hope this makes sense.

Thanks, Mark.