How do I delete mails from Mail Queue Manager in WHM?

The Mail Queue Manager allows you to view, delete, and attempt to deliver queued messages that the system has not yet delivered to their destinations. For example, the system places messages in your mail queue if the sender addressed the messages to invalid hosts or addresses.

If you want to resend the queued mails you can follow the below procedure,

Once the mail delivered or get deleted it will not present in WHM mail queue.