Postfix
Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers email. This is required in order to be able to send emails from a local machine (without using any vendor’s client).
Installation
Postfix has to be configured. The suggested way to do that is via: sudo dpkg-reconfigure postfix. You can also directly edit your /etc/postfix/main.cf file and make changes to the configuration. For most purposes, dpkg-reconfigure should suffice.