How to create your own mail server

https://www.digitalocean.com/community/tutorials/why-you-may-not-want-to-run-your-own-mail-server

https://www.digitalocean.com/community/tutorials/how-to-configure-a-mail-server-using-postfix-dovecot-mysql-and-spamassasin

https://www.digitalocean.com/community/tutorials/how-to-run-your-own-mail-server-with-mail-in-a-box-on-ubuntu-14-04