Assistance with doveadm backup...

I am having trouble locating examples of how to use doveadm backup. All the examples I see are for sync. I simply want to create a backup to a network volume of the email server's vmail folders. The goal here is to have a reasonably current backup should the main drive on the email server go south.

We currently authenticate our users from a mysql database. User’s mailboxes are stored as domainname/username/Maildir

I assume what I will wind up on the network volume is a duplicate directory structure as the vmail folder on the email server?

Can someone help get me started here?

Jeff