If the sendmail package is removed and reinstalled, which currently
happens on every upgrade due to pkg(8) split upgrade issues, smmsp
will stop working because its open handle to /var/spool/mqueue is no
longer valid after pkg removes and recreates this directory.
Work around this by using a trigger to restart sendmail after upgrading
it, if /var/spool/{client,}mqueue has changed.
MFC after: 3 days