Which command, available with all MTAs, is used to list the contents of the MTA’s mail queue?
(Specify ONLY the command without any path or parameters.)

Answer: See the explanation

Explanation:
mailq, /usr/bin/mailq, sendmail -bp, /usr/sbin/sendmail -bp, /usr/lib/sendmail -bp,
sendmail, /usr/sbin/sendmail, /usr/lib/sendmail