Send email via FB username. firstname.lastname@example.org is your facebook email id. If you want to send email by FB email id then Open Messages > New Message >TO – mail id (email@example.com) & Message– ‘Your message’ > SEND.
With the text message it allows you to send files as well as a photo. But it does not support normail eMail features like Subject, Bcc, cc etc.
How do I get facebook Email Id?
If you want to check your FB email id or you want to create/edit your Username. Open Account Setting > Click on Username > Here you can create/edit your username and check your FB email id.