One day, I'll be able to write this up for DigitalOcean, and get some credit for my account: Write For DigitalOcean Share Your Technical Expertise!. But that's gong to take too long!

Documentation

• DigitalOcean Community Documentation (e-mail) 20.04:
  • How To Install and Configure Postfix on Ubuntu 20.04
• DigitalOcean Community Documentation (e-mail) Original:
  • How To Install and Configure Postfix on Ubuntu 16.04
  • Part 1: How To Set Up a Postfix E-Mail Server with Dovecot
  • Part 2: How To Set Up a Postfix Email Server with Dovecot: Dynamic Maildirs and LMTP

Various links used in debugging under older installation

• Suppresss “~/Mail does not exist” in mutt. Just create the dir and have done with it.
• Is it ok to use self-signed certificates for smtp transport?
• Test sender TLS
• Postfix emails send outgoing mail with wrong domain name
• How do I change the hostname without a restart? - sudo hostname roman-halliday.com
• How To Create a SPF Record For Your Domain with Google Apps

Email server testing site:

• https://mxtoolbox.com/domain/roman-halliday.com/