remove username string for Horde login

Hello all

I have Horde webmail with Virtualmin gpl.

When I create a new email account, virtualmin create a user like this:

user.domain

"user" this is the pop3 and imap user for "domain"

then when I log in to horde I must use "user.domain" like username.

That's works, but I would like to use only "user" or "user@domain" not "user.domain".

I would like to remove ".domain" from my usernames when use horde with virtualmin.

Excuse my english and thanks a lot for any help.

roberto