Here's how to find secret messages in Facebook's hidden inbox

There's a secret folder on Facebook Messenger containing messages that you probably didn't know existed.

Some of them can be vitally important, with one Facebook user, Daniel Emery, only discovering his friend had died after checking this folder.

When you receive a message from someone on Facebook who isn't your friend, Facebook alerts you to let you know. But the social-media network doesn't do this for every message you receive from a non-Facebook friend.

If Facebook thinks the message is spam, it will tuck it away into a hidden vault.

Several Business Insider journalists found the vault, and all of us had messages in there that we didn't know we had ever received.

Here's how to find the secret vault: