jmtd → software → halfcoded → mail-prefs
a mail-prefs debian package which lets the system administrator set their preferred mailbox format for system mailboxes; mbox or maildir (or mh or whatever). Then, mutt, exim4, etc. could use this key to determine what config to use, rather than either make the (wrong) assumption or prompt the user, again.
They'd need to pre-depend on mail-prefs most likely.