squeeze and crypt

Hi,

I am using vexim on several debian-exim4 machines for a couple of years now 
and I am very happy with it.
However, since I upgraded some of the machines to debian 6.0 squeeze there 
seems to be a problem with the encrypted passwords. On password creation or 
change the "crypt" field in the users-table stays empty.
I can correct this manually but doing that for all of my users is not 
something I want to do forever.
I checked the vexim code and everything seems to be alright, I wasn't able 
to find the problem.

Since I suppose this problem will occur on all squeeze machines I hoped 
someone already has a fix for it.
Can you help me with that?

Regards,

Chris