How do I encrypt emails sent from my server?

The past days I have been working on setting up Email on my server, I have manged to send emails (without them going to the spam folder) but the emails are still not being encrypted.

The server is Ubuntu 16.04 with Apache2 (LAMP stack) - and right now I am sending emails without SMTP (i think) I’m using PHPMailer to send emails.

Here’s the tutorials I have followed: https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-as-a-send-only-smtp-server-on-ubuntu-16-04 https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy https://www.digitalocean.com/community/tutorials/how-to-use-an-spf-record-to-prevent-spoofing-improve-e-mail-reliability

For encryption I tried these tutorials, but they didn’t help. https://www.digitalocean.com/community/tutorials/how-to-use-gpg-to-encrypt-and-sign-messages https://www.digitalocean.com/community/tutorials/how-to-setup-additional-entropy-for-cloud-servers-using-haveged

Can anyone point me in the right direction? Thanks.