As qmail service is corrupt on the server then we can reconfigure it by using the following steps but make sure that you have logged in as root user.
Stop the running mail services.
/etc/init.d/qmail stop
/etc/init.d/xinetd stop
Now take the backup for the existing qmail to ignore any data loss issue.
mv /var/qmail/queue /var/qmail/queue_old
Now check which qmail rpm we are using on the server
rpm -q psa-qmail
As soon as you confirm the installed qmail rpm, select the rpm from the following URL as per the Plesk version and server OS.
http://autoinstall.pp.parallels.com/
For example we are using the Plesk 9.0.1 and cetnOS 5.6 with 32BIT
rpm -Uvh –force http://autoinstall.pp.parallels.com/PSA_9.0.1/dist-rpm-CentOS-5-i386/opt/maildrivers/psa-qmail-1.03-cos5.build90090127.18.i586.rpm
Now restart the mails services
/etc/init.d/qmail start
/etc/init.d/xinetd start
