There are two new buttons for the Private Messages folders.
Check All
This button is used to select all of the messages, both read and unread, on the current page of a folder. It does not select messages on other pages. You can delete the selected messages by clicking on the Delete button, marked them as read by clicking on the Mark As Read button, or move them to another folder with the Mover Items to Folder..... menu.
If you click on the Check All button, it will become a Clear All button. Clicking on the Clear All button will deselect the chosen messages. You can also manually deselect individual messages by clicking in its checkbox.
Delete All
This button will delete all read messages in the a folder. This action is not limited to the current page; it is applied to all read messages in the folder. Unread messages will not be deleted.
Clicking on the Delete All button will produce a confirmation window similar to this one.
Although the warning messages says "will permanently delete," that is true only if you are in the Trash folder. For other folders, if you confirm the action by clicking on the OK button, all of the read messages in the folder will be moved to the trash can. If you are in the Trash folder, the messages will be permanently deleted.
Clicking on the Cancel button will cancel the action.
I deleted all of the messages in a folder, but didn't mean to.
Open the Trash folder and select the messages you didn't mean to delete. You can use the Move Items to Folder.... menu to move them back to any folder, except the Inbox
The original post was written to be added to the FAQs at the top of Forum Technical Support. If you have suggestions or questions about things that need to be clarified, please add them to this thread. I will attempt to incorporated them into the post.