Hi,
I am not sure if AD support this, but if you can run a script on Linux once a user change the Password in AD, than you can change user password easily.
I am not aware of the setup you have nor i hae experince on qmail and AD
, but as programmer, I am sure that when you change AD password you can have some sort of event capturing, you need to trigger a script that change the Virtual password.
Also, I am interesting to know how you set those thing, as I am also looking for same solution for my company
If you can help me setting up that, thanks