เมื่อ Qmail เกิดปัญหา:
alert: cannot start: unable to open mutex
แก้ด้วย:
mkdir /usr/local/psa/qmail/queue/lock
touch /usr/local/psa/qmail/queue/lock/sendmutex
chown qmails:qmail /usr/local/psa/qmail/queue/lock/sendmutex
chown qmails:qmail /usr/local/psa/qmail/queue/lock/
chmod 777 /usr/local/psa/qmail/queue/lock