doveadm expunge: Improved the error hint message about using something else besides MAILBOX.
doveadm expunge: Improved the error hint message about using something else besides MAILBOX.

jkerihuel/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jwm/dovecot-notmuch