"Linux distributions have relied on the venerable Sendmail
package since the early days of Slackware. But Sendmail's rich mail
server features aren't an ideal solution for the typical desktop
user whose primary mail support is delivered through a remote ISP.
That's the perfect place for a simpler solution: sSMTP.
"Many years ago, before the Internet standardized on Simple Mail
Transfer Protocol (SMTP), applications known as mail transfer
agents (MTA) were designed to help process email and determine the
best route for message delivery..."