Backing Up and Restoring mailboxes

I am going to be wiping clean my system and doing a complete upgrade. I have dovecot installed. I want to back up the mail system, and then be able to restore it.

I thought that I could do this.

doveadm -Dv backup -u user@example.com maildir:~/DoveBU

Then I was going to gunzip that directory and put it onto a USB Drive.

Now, after updating the system, I thought that I could just unzip the file from the USB drive. My question is, what command do I run to return the files to the same place they were originally. Assuming the structure was: "/var/mail/vmail/", what would I do?

Thanks

-- Jerry