Which of the following commands should be used to print a listing of email in the system's mail queue?

`lpq` is used to display the status of print queues, not email queues.

The `mailq` command is specifically designed and commonly used to display the contents of the mail queue, providing information about messages that are waiting to be sent or delivered by the system's Mail Transfer Agent (MTA).

`mlq` is not a standard or recognized command for viewing mail queues.

`sendmail -l` typically relates to logging levels or daemon options for the `sendmail` MTA, and it does not list the mail queue; the equivalent to `mailq` using `sendmail` would be `sendmail -bp`.