In Facebook, now you can also recover your deleted messages or a group of messages from your inbox which can be your recieved or sent messages or simply updates from the different pages that you have joined. It’s not a trick or anything like it, rather it’s just a feature added by Facebook without any notification or update in their official blog.
To recover a deleted message, find the link of undo in a yellow box below the button of “+ Compose”. Check out the screen Shot below.
This link will appear in your inbox whenever you delete one or more of messages that might be received or sent messages. You can also undo the deleted updates from the pages. This feature helps to clean inbox faster as you don’t have to confirm “are you sure want to delete this message” every time, but you still don’t have an option of recovering an old deleted message that you have deleted a long while ago. However to read an old message that is no more in your inbox, you can check your e-mails as Facebook always send you an e-mail notification in your mailbox whenever you recieves a new message.