Now you can use your PGP key to encrypt email sent by Facebook.
How can you do it:
1. Login to you Facebook account.
2. Go to PGP Public KeyYour profile > About > Contact & Basic info > PGP Public Key
3. Past your public key.
4. Facebook will sent you an encrypted verification mail. Check and aggree to that mail.
5. You will get final confirmation.
If any one get access to your email account; they can’t read though your facebook mail or message (hopefully they will not access to your private key or passphrase). Even if they hack your email account.