PGP, and its free version GnuPG, are protocols that allow you to encrypt emails from end to end. When you send an email, it is stored unencrypted on your and your recipient mail servers. If someone else accesses any of the two accounts - through an attack or with a court order - they can access the content of all emails received or sent. But if the email has been encrypted with PGP or GnuPG, only those who know the password to decrypt a message and have the file that accompanies it, as a key, can access its content. In addition, this protocols allows you to verify the identity of the sender through digital signatures, thus avoiding impersonation. Check encrypted email.