Sadly not.
"zmmailboxmove" is only available in the network edition.
I don't have found a command in the open source edition that does the same
The only way i have found is to backup the users E-Mails, then delete the user create an new user with the new E-Mailserver and write the backup to the new mailbox.
Is there a better way to do this in open source edition?
yogg