The messaging service of Facebook acts much like a typical e-mail service. Messages can be contained in a message thread that begins with the first message sent and includes all replies from recipient and sender. These message threads compose a history of communication on Facebook. You can delete the history of messages that you have sent to others' in-boxes on Facebook by deleting a specific message thread. Deleting a message history can keep your mailbox from being cluttered and will erase any unwanted conversations.
Log into your Facebook account on the home page. Enter the registered e-mail address and your password for your account. Click the "Login" button. This will take you to your home page.
Click on the "Messages" icon located at the left-hand top of the page, between the Facebook letterhead and the search box. The icon is shaped like two opposing cartoon speech boxes. A window will appear with your most recent messages. Click on the "See All Messages" option at the bottom of the window. This will take you to your message centre. You can also click on the "Messages" option underneath your profile photo on the left-hand side of the page.
Click on the "Sent" option in the left-hand side menu, underneath the "Messages" title. This will bring up the history of the messages that you have sent to another Facebook user.
Press the left- and right-facing arrows at the top and bottom right of the page to access another page of messages. Type the subject or a keyword of the desired message thread into the search box and click the magnifying glass icon to bring up a specific message thread.
Click on the "X" to the right of the message thread to delete the messages and their history. This will delete all the messages that you have sent and received in this message thread. Also, click on the box to the right of the recipient, and click on the "Delete" button at the top of the messages to delete the thread and history.
Clicking on the "X" next to messages in your inbox will also delete the history of replied messages.
Double-check that the message history that you are deleting is the right one. Once the history has been deleted, it cannot be retrieved. You can only delete messages from your mailbox. Deleting your history of messages sent will not delete the recipient's messages.