Kolab delegation in Roundcube

[Thomas Reitelbach]

Hello list,

I'm investigating Roundcube in Kolab 3.1 as new standard mail client for my 
users.
But I'm stuck with configuring Mail Delegation.

I have configured a user info at mydomain.de and share his INBOX and Calendar via 
ACLs to all my users.
Also I have setup some delegates in the Web Administration Panel for the user 
info at mydomain.de.

My users should be allowed to send messages in behalf of info at mydomain.de. 

I believe I have to configure a new Identity in Roundcube with the sender 
address "info at mydomain.de" for my users, but how would I do that in roundcube?
The configuration options for "new identity" does not allow me to use a user-
defined mail address as sender. I can only choose from a dropdown-list which 
includes only the primary and secondary mail address of the respective user, 
but not the info at mydomain.de address.

Any clues?

Don't know if this is important, but I'm using the multiDomain-Scripts from 
TBITS.

Thank you in advance
Thomas