How to setup Postfix mail server on Ubuntu using SquirrelMail ?

The postfix mail server is an open-source MTA (mail transfer agent). Postfix routes e-mails to the desired mail server. It was originally released in 1998 and still active in 2019. It is also known as VMailer or IBM secure mail. If you don’t want to use mail servers like G-mail and want to convert your Ubuntu machine into a mail server then you are at the right place.