Plesk uses Qmail as mail server on Linux server.
Here are some useful commands related to Qmail mail server.
Hope you find them informative and helpful !
1) Start Qmail service
# service qmail start
2) Stop Qmail service
# service qmail stop
3) Status of Qmail service
# service qmail status
4) Qmail log on Plesk server
5) To view the amount of messages currently in your outbound queue
6)To list out all messages in your outbound queue
7) To read the entire contents of an email, including headers, where NNNN is the 8 digit ID specified on the /var/qmail/bin/qmail-qread command
# find /var/qmail/queue -name NNNN| xargs cat | less
8.) To remove specific mails from mail queue
(requires qmail-remove install on server)
#qmail-remove -r -p
# qmail-remove -r -p xyz.com
This will remove all emails in queue with “xyz.com” in it
9) Mailbox location in Plesk
If any feedback, queries are always welcome!