Security Strategies in Linux Platforms and Applications, 3rd Edition

Mail Transfer Agents

Email client applications such as Evolution and Thunderbird are known as mail user agents (MUAs). Services such as fetchmail that collect email from networks are known as mail retrieval agents (MRAs). Email services that send such mail along to client applications are known as mail delivery agents (MDAs). When email client applications send messages for delivery, they use mail transfer agents (MTAs) such as Exim, Sendmail, and Postfix.

Sendmail is both an application and a company. The company offers enterprise mail solutions, founded on the application, which has long been an open-source mail transfer agent. Sendmail has been around as a mail transfer agent for decades, and it was long considered the de facto MTA for many ...