You can use an IMAP server to auto create users and e-mail accounts.
- Install the imapauthenticator module at Start menu -> Modules
- Reload Group-Office
Go to System Settings -> Authentication. There's a new IMAP Autentication section there.
Click on the add button to add a new IMAP server profile:
Now you should be able to login with the full e-mail address. You can't change passwords with Group-Office using this autentication method.