This feature will allow you to view all of your mailboxes and remove any old or large messages. This is a great option when you have 100's of emails with in any of your folders and don't have the time click on each one to delete them.
To use this option you will first need to log into your cPanel and scroll down to the "EMAIL" section and click on the "Email Disk Usage" icon.
The page that loads up will be similar to the screen shot below. You are able to change the email address that you are view by clicking the drop down option and clicking on the email address you want to manage.
Click on the option "Manage" of the mailbox that you want to remove email for it to drop down your options. From here you are able to select what parameter for the messages that you want to delete permanently.
Once you have selected the parameter you can click on "Delete Permanently". It will take some time to complete the task depending on how much email there are in the mailbox. Once it has removed the email it will give you a confirmation on the top right corner of the page.