The mailq command is a widely used tool for checking the email queue in Linux. It provides a summary of all the messages in the queue, including information such as message IDs, sender addresses, recipient addresses, and delivery status1. The mail queue is a collection of messages that are waiting to be delivered by the local Mail Transfer Agent (MTA), such as sendmail, postfix, or exim1. The mailq command is the same as the sendmail -bp command that also prints the mail queue2. The mailq command can also accept various options to filter or modify the output, such as -v for verbose mode, -Ac for mail submission queue, or -q for processing the queue3. The mailq command is part of the LPI's multi-level Linux professional certification program, and it is covered in the topic 108.3 Mail Transfer Agent (MTA) basics of the exam 102 objectives4. Reference: 4: https://www.lpi.org/our-certifications/exam-102-objectives/ 3: https://www.thegeekdiary.com/mailq-command-examples-in-linux/ 2: https://sites.ualberta.ca/dept/chemeng/AIX-43/share/man/info/C/a_doc_lib/cmds/aixcmds3/mailq.htm 1: https://www.emaillistvalidation.com/blog/check-email-queue-in-linux-a-comprehensive-guide-to-managing-message-queues/