Email encryption is a term that refers to the encryption as well as the authentication of email or electronic mail messages. Most commonly, email encryption is designed to rely on what is known as public key cryptography. There are a number of popular protocols that are used for the purpose of email encryption, the most notable of which are mail session encryption, identity based encryption, Open PGP encryption, TLS encryption and S/MIME encryption.

- Mail Session Encryption - This involves using a STARTTLS SMTP extension, which is a TLS layer that is on top of an SMTP connection. It is capable of protecting mail traffic from being sniffed while it is being transmitted, but this does not actually involve encrypting the actual email because the content inside the email messages is capable of being revealed to, and thusly tampered with, by the email relays that are involved. The encryption, then, actually occurs between the individual SMTP relays rather than between the individual sender and recipient. When both of the relays offer support for STARTTLS, then it is capable of being used regardless of whether or not another protocol is being used to encrypt the contents of the email.

- Identity Based Encryption is a form of public key cryptography that is designed and implemented to use unique information regarding the identity of the user such as their email address as the public key. The public key may also be a text value such as the domain name or name or its associated IP address for example.

- Open PGP - PGP stands for Pretty Good Privacy, and Open PGP is a computer program designed to provide cryptographic privacy as well as authentication. It is often utilized for the purpose of signing, decrypting or encrypting emails in order to increase the level of security for email communication.

- TLS - TLS stands for Transport Layer Security, and it is the successor to Secure Sockets Layer or SSL. These are cryptographic protocols designed to provide data integrity and security for network communications such as through the internet. There are a number of different versions of these protocols that see wide spread use including web browsing, internet faxing, electronic mail, VoIP and instant messaging.

- S/MIME - S/MIME is an acronym that stands for Secure Multipurpose Internet Mail Extensions, and this is a standard that is used for signing email and public key encryption of email that is encapsulated in MIME.

A Private Email Network , PEN is a secure pathway that employs highly effective encryption, without requiring complex programs, certificates or servers. Secure messages use existing e-mail address and can be created and read in any systems. Email2 is a business communication platform that enables security for your organization and creates a Private Email Network

Each of these email encryption protocols, mail session encryption, identity based encryption, Open PGP encryption, TLS encryption and S/MIME encryption are used for different purposes and some apply not only to email encryption but also to other types of encryption including internet browsing and instant messaging encryption depending on the method and mode of communication.