combrk Take a look at post #8 [https://community.grommunio.com/d/1444-suchfunktion-in-webapp-deskapp-mit-fehlermeldung/8]. This should help you migrate your data set. These instructions were created for moving from one Grommunio appliance to a new one, so if you are not using the appliance you might have t adapt slightly but it should get you covering the main parts. Also this only covers migration of the mail (and possibly files if you use it) and the relevant databases.
EDIT: If you are changing hypervisor (sorry missed that bit), it depends on if you are using the appliance at the moment or not and also how much customisation of this, like Postfix, you have done to your original VM. If not much customisation, and using the appliance, build a new Grommunio VM in your new hypervisor, and migrate data as above. Then copy any customisation you may have done (should be in your build docs).
@Andy posted an adaptation of the above migration process a couple of weeks ago that included copying some config files around but I can't remember the exact post that was it, perhaps @Andy can refer you.
Hope above helps.