By default Qmail allows a maximum of 10 local and 20 remote deliveries of emails simultaneously. In order to increase the number of concurrent local and remote email deliveries in Qmail, the values in the concurrencylocal and concurrencyremote files needed to be increased.
Plesk control panel also offers Qmail and have the same default values and location of the files.
The concurrencylocal and concurrencyremote files resides under the /var/qmail/control directory. If the files are not present, you need to create them
# vi /var/qmail/control/concurrencylocal # vi /var/qmail/control/concurrencyremote
set a value as per your wish. For the new values to take affect, restart the qmail service
# service qmail restart
Once done, you can manage the Qmail mail queue using Qmhandle.
