Sendmail is an open source smtp server. Many different languages and frameworks interface with sendmail, and when debugging it's good to be able to quickly test whether or not sendmail is working.

The following is a quick way to verify that sendmail is working.

echo "Subject: test" | /usr/lib/sendmail -v
Zach Zach (248)

Naming things is hard. "There are only two hard problems in Computer Science: cache invalidation and naming things." — Phil Karlton Truer words were never spoken.