Dovecot's home directory is a user-specific state
directory, see https://doc.dovecot.org/2.3/configuration_manual/home_directories_for_virtual_users/.
It is recommendated
1. to never configure a userdb to return the same
home directory for multiple users
2. to store the mailbox under the home directory,
e.g. home = /var/vmail/domain/user and
mail = /var/vmail/domain/user/mail
This change implements these recommendations. The
mailboxes are now stored at
<mailDirectory>/<domain>/<user>/mail. Existing
mailboxes are moved automatically to the new
location as part of the ExecStartPre hook of
dovecot's systemd unit.
Christian Ulrich
93e2e9395c