Moving storage of mail from one volume to another

I need to move all mail and the users from one volume to another. I have added extra mail storage to the set up, but now I would like to move all mail to new directory.

In workgroup manager I have set "alternate partition" to mailstorage, and new folders adds to this place for all users, but the old mail is at the old place, and this is growing.

I have earlier tried to move the mail by telling server admin a new place, but that was not lucky, it did not accept a new location.

Do anybody know how to do this?