sending as kolab distribution list member

[hede]

Hi,

I have some kolab distribution lists (group) and would like to be able to send in behalf of the list/groups email address. 

Like for example, if I have a "user1" belonging to the kolab distribution list "group1", if user1 sends an email with Identity group1, it doesn't work:

554 5.7.1 <DATA>: Data command rejected: uid=user1,ou=People,dc=example,dc=com is unauthorized to send on behalf of cn=group1,ou=Groups,dc=example,dc=com

On the other hand, if I also add group1 at example.com as an alias for user1, then he is able to send mails on behalf of group1, but then the distribution list doesn't work: only user1 gets mails to group1.

Any hints to solve this? Maybe postfix should first look for groups before resolving aliases? How to do so? 

regards
hede