DESCRIPTIONqmail-newmrh reads the instructions in /var/lib/qmail/control/morercpthosts and writes them into /var/lib/qmail/control/morercpthosts.cdb in a binary format suited for quick access by qmail-smtpd.
If there is a problem with control/morercpthosts, qmail-newmrh complains and leaves control/morercpthosts.cdb alone.
qmail-newmrh ensures that control/morercpthosts.cdb is updated atomically, so qmail-smtpd never has to wait for qmail-newmrh to finish. However, qmail-newmrh makes no attempt to protect against two simultaneous updates of control/morercpthosts.cdb.
The binary control/morercpthosts.cdb format is portable across machines.