The Perfect Server – Ubuntu 16.04 (Xenial Xerus) with Apache, PHP, MySQL, PureFTPD, BIND, Postfix, Dovecot and ISPConfig 3.1 https://www.howtoforge.com/tutorial/perfect-server-ubuntu-16.04-with-apache-php-myqsl-pureftpd-bind-postfix-doveot-and-ispconfig/
How To Install and Configure Postfix on Ubuntu 16.04 | DigitalOcean https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-on-ubuntu-16-04
Configure Postfix to Use Gmail SMTP on Ubuntu – EasyEngine https://easyengine.io/tutorials/linux/ubuntu-postfix-gmail-smtp/
Email sent to gmail is flagged as spam. | DigitalOcean https://www.digitalocean.com/community/questions/email-sent-to-gmail-is-flagged-as-spam
How To Install and Configure Postfix as a Send-Only SMTP Server on Ubuntu 14.04 | DigitalOcean https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-as-a-send-only-smtp-server-on-ubuntu-14-04
10.04 – How can I disable postfix on startup? – Ask Ubuntu http://askubuntu.com/questions/231402/how-can-i-disable-postfix-on-startup