Change and move Maildir

Hello,

I have a problem with disk space, 2x 1.5 TB ssd RAID1 are too small for tons mail that i have to handle.
I came up with the idea to buy 2x 6TB hdd drives and mount it with RAID1, but how to change mailboxes directory and how to move 1,1TB existing mailboxes? Actually they stored in /home/username/homes/mailuser_name/

I’d copy all of /home/* to a partition or volume on the new drive(s) and mount it on /home.