The central webmail retains contacts regardless of which mail server the customer is on. The per-server webmail at https://mail.customerdomain does not retain contacts during a server move. However they can almost certainly be moved manually.
If the destination server is a fresh server which had no previous customers, you could copy the entire sqlite database. It is stored in ~roundcubelocal/db.sqlite
on both servers, just copy it from one to the other but make sure it remains owned by the roundcubelocal
user. If you need to merge the contacts from 2 servers then please send a support ticket and we will try to assist.
In future a role migration through Enhance will copy the contacts, we're aware this is a functionality gap.