Here are some useful Qmail commands that you can use in shell:
To start qmail service:
# service qmail start
To stop qmail service:
# service qmail stop
Server with Plesk qmail log location:
# /usr/local/psa/var/log/maillog
To view the amount of messages currently in the queue:
# /var/qmail/bin/qmail-qstat
To list out all messages in your outbound queue:
# /var/qmail/bin/qmail-qread
For servers with Plesk mailbox location:
# /var/qmail/mailnames
To read the entire contents of an email, including headers:
# find /var/qmail/queue -name XXXX | xargs cat | less
To remove specific mails from mail queue:
# qmail-remove -r -p xyz.com
Qmail hostname config file location:
/var/qmail/control/me