Sorry, different email client on the road.

I created the folders under my dovecot install /usr/local/etc/dovecot/virtual/ and then created month and day folders with dovecot-virtaul files in each folder. The folders how up on the mail clients, but either are inaccessible, or empty.

namespace {

  prefix = @virtual.

 separator = .

 location = virtual:/usr/local/etc/dovecot/virtual:INDEX=˜/Maildir/virtual:CONTROL:˜/Maildir/virtual

}