Nowadays, anyone who tries to send you a private message without being your friend on Facebook will instead send a "message request," which the recipient can read and then decide whether they want to allow any communication.
However, there's still a way you could be missing messages. Because there's ANOTHER secret folder.
Essentially, Facebook appears to "filter" some message requests, similarly to the spam folder of your email inbox. But you never know, some of these messages could be useful, especially if you're using your Facebook profile for professional purposes.
Anyway, here's how to unlock it and check whether you've been inadvertently withholding certain messages, with the help of some very professionally-drawn red arrows.
Head to the Facebook Messenger App.
Click "Settings" in the bottom right-hand corner.
Click "Message requests."
And underneath all the message requests you've been sent, will be an option for "See filtered requests."
In here, you'll find all the messages you hadn't been sent a request for in bold.
So there you go. Enjoy your new unfiltered messaging life.