[imp] virtual domain choose at login

[Puramukas]

Is there any way to make to add a default domain based on which server is 
selected at login time, so that  there will be no need to type 
jhon at example.com but only john and the example.com will be added 
automatcally based on the server which is choosed at login time? because by 
default
if you choose a server and try to login only with user name john, the added 
example.com is always the same no matter what server you choosed.