Neomail user preferences Domain List, Domain Locking

In the neomail preferences, I noticed that I either have to supply domain names for my users to choose from or I have to lock them into a domain.  This can be too much work when I am adding users with mqany different domains.  I do not want to be editing the neomail config file each time I iget a new customer.

I need to know of a way to allow a user to be able to type in their full email address that I give them when they fill out their initial preferences on first time login.  I do not want the drop down box.

Do I need to make a change to the code to accomplish this?  Just trying to make my tasks of adding new customers easier and the last thing I need is another file to edit. 

Please respond only if you have or know how to accomplish this.

Thank You

Jason