Postfix virtual domains and users on CentOS with mariadb Godaddy VPS Letsencrypt ssl plone 5 apache
Basic postfix install: https://likegeeks.com/linux-mail-server/
centos with maria (with postfixadmin 3.0.2)
https://www.rosehosting.com/blog/set-up-a-mail-server-with-postfixadmin-and-mariadb-on-centos-7/
Some tweaks for postfixadmin 3.2 (though Ubuntu, still applicable to centos):
https://linoxide.com/mail/install-configure-postfix-ubuntu/
Godaddy about PTR reverse DNS
https://www.godaddy.com/help/what-is-reverse-dns-2585
Dovecot
Install and configure Dovecot on CentOS
https://support.rackspace.com/how-to/dovecot-installation-and-configuration-on-centos/
Virtual user mail system with Postfix, Dovecot and Roundcube
https://wiki.archlinux.org/index.php/Virtual_user_mail_system_with_Postfix,_Dovecot_and_Roundcube
LetsEncrypt CertBot
https://wiki.archlinux.org/index.php/Certbot
https://docs.plone.org/manage/deploying/front-end/apache.html
Test page speed: https://varvy.com/pagespeed/enable-compression.html
https://varvy.com/pagespeed/
https://help.ubuntu.com/community/PostfixCompleteVirtualMailSystemHowto
https://support.rackspace.com/how-to/dovecot-installation-and-configuration-on-centos/
Horde Install
https://www.horde.org/apps/horde/docs/INSTALL
Letencrypt
https://certbot.eff.org/lets-encrypt/centosrhel7-apache
Dovecot and Postfix with virtual domain users.
https://www.tecmint.com/configure-postfix-and-dovecot-with-virtual-domain-users-in-linux/