An email account has gotten full and the user wants to remove their old messages without having to delete them one at a time in webmail.
Log into webmail and click on the pie chart with disk use information to access the interface:
Click on the "Manage" option on the far right next to the folder you wish to remove messages from.
Select the option that describes what you want to delete. Click "Delete Permanently". Do note that this does NOT move messages to the Trash, but totally removes them in a way such that they cannot be retrieved later. It is not possible to undo this delete, so be sure you have selected the correct option before clicking "Delete Permanently".
Our documentation for this feature can be found at docs.cpanel.net.