The social network Facebook changes arbitrarily, millions of email addresses of its customers in each profile.
For example, if the mail was @gmail.com before, now it turns to @facebook.com.
All platform users now have an address with the domain name Facebook, even if they don’t want one. When someone sends you a message, it will no longer be received in your personal email address but into the new messaging system of Facebook, which you should check frequently if you want to read the letter.
The new contact details are displayed automatically in the profile or timeline of each user, while the old email is gone.