Displays the current mail queue. In best case this is always empty. The mail queue contains mails which the mail server has not already delivered because of different reasons. You will find the respective reason printed within each line. You can force the mail server to start delivery of the mail queue by pressing the button . Please don't expect that the mail queue turns empty after doing that. This just starts delivery. If the mail server again is unable to deliver some mails they will rest in the mail queue until expiration.