Linux Journal: Securing Sendmail with TLS

“One of the most common uses of network systems is for
e-mail-based communications. As such, a great deal of attention has
been given to securing e-mail systems. However, most of this focus
has been in two areas: security at the message level, using PGP or
S/MIME, and confidentiality in the authentication process for mail
retrieval, i.e., using APOP or SSL-based IMAP. This still leaves
mail server-to-server traversal vulnerable to several attacks.

The introduction of basic cryptography into a mail
server-to-server session alleviates most of these risks. Mail
transport agents (MTA) and software such as Sendmail or Postfix can
be augmented to handle their communications over transaction layer
security (TLS) channels. This provides for a number of services,
including confidentiality, integrity protection and strong
authentication.

This article will introduce the features and use of SMTP over
TLS as defined in RFC 2487, as well as illustrate their setup in
the Sendmail package. We will cover cryptography basics, though not
delve into the mathematics of cryptosystems and simple mail
transfer protocol (SMTP) and extended simple mail transfer protocol
(ESMTP) basics.”

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