Email Security

Email security overlaps with file security and, as discussed later, with network security. GnuPG is the tool most frequently used for email security, although you can also use PGP. PEM (Privacy Enhanced Mail) is a standard rather than an algorithm and is used less frequently.

MTAs (Mail Transfer Agents)

An increasingly commonplace MTA is STARTTLS (Start Transport Layer Security; www.sendmail.org/~ca/email/starttls.html). TLS itself usually refers to SSL (Secure Sockets Layer) and has become the de facto method for encrypting TCP/IP traffic on the Internet. The sendmail daemon can be built to support STARTTLS, and much documentation exists on how to do so. STARTTLS enhancements also exist for qmail and postfix and other popular MTAs. It is important to recognize that this capability provides encryption between two mail servers but not necessarily between your machine and the mail server. Also, the advantages of using TLS are negated if the email must pass through a relay that does not support TLS.

MUAs (Mail User Agents)

Many popular mail user agents, such as mutt, elm, and emacs, include the ability to use PGP or GnuPG for encryption. This approach has become the default way to exchange secure email.