Email is still the #1 app on the internet.
I list below free and open source solutions to email. You need not consider the closed source alternatives. They are dramatically inferior in a number of ways.
- Google Hosted: Have Google serve your email need.
Other hosting providers will provide one or more of the free options I list below.
- Sendmail: Sendmail is the 500lb gorilla in email. There are other systems, but sendmail remains the most relied on tool to send email.