[imp] imp / imap username problem

[Martin]

Hi, im using horde/imp 3 

with "net" qmail 1.05 and latest stable vpopmail.
For imap I use latest stable courier-imap. 

I know others have had this problem, however a working
solution hasen't - to my knowledge - come along. 

My problem is that I'am running vpopmail and have several domains. 

To get the from addresses right in imp I've added
a server for every virtual domain in ./imp/config/servers.php
 - eg. even though it is the same server the maildomain needs to change. 

When users log in the select their server (eg. virtual domain)
from the server list on the imp login.php.
My problem is that they still need to supply user at virtualdomain.tld
in the username field - because the imap - hence, vpopmail needs this! 

As far as I can tell I need for horde to change the supplied username before 
sending it to the imap server. 

I have searched the imp mailling list and I think I need
a hook in /horde/config/hooks.php -
This hook needs to get the maildomain value for the selected server on
the login page and append it with an @ to the username.
...and ofcourse then to enable vhooks in the con.php 

However I don't know how to get the maildomain from the selected server on 
the loginpage, there's no examples in the hooks.php for something like this. 

Any help is welcome. 

Thanks in advance. 

Best regards, Martin