==== GMail as a Relay on Linux Ubunutu 20.04 LTS and CENTOS8 ====

Using Postfix for this solution.

Follow instructions at https://www.linode.com/docs/guides/configure-postfix-to-send-mail-using-gmail-and-google-workspace-on-debian-or-ubuntu/ 

Or see the same at {{ ::sending_emails_using_postfix_from_your_linux_server.pdf|Sending Emails Using Postfix From Your Linux Server}}

  * Will this also break with less sure apps?
    * The "Less Secure Apps" is not available in Gmail if your account is configured for 2-factor authentication
    * Everything should work OK.

For CENTOS8:

  dnf install postfix ca-certificates mutt
  dnf install cyrus-sasl, cyrus-sasl-gssapi, cyrus-sasl-lib, cyrus-sasl-plain
  systemctl start postfix
  systemctl enable postfix

Next perform the following steps as root:
  
  cd /etc/postfix
  cp main.cf main.cf.distro
  mkdir /etc/postfix/sasl
  cd /etc/postfix/sasl
  vi sasl_passwd

Add this line:

  [smtp.gmail.com]:587 username@gmail.com:password

  postmap /etc/postfix/sasl/sasl_passwd
  chown root:root /etc/postfix/sasl/sasl_passwd /etc/postfix/sasl/sasl_passwd.db
  chmod 0600 /etc/postfix/sasl/sasl_passwd /etc/postfix/sasl/sasl_passwd.db

  vi /etc/postfix/main.cf

Comment out this line:

  #smtp_tls_security_level = may

Now wdd to the end of the main.cf file:

  # Local Edits
  relayhost = [smtp.gmail.com]:587
  # Enable SASL authentication
  smtp_sasl_auth_enable = yes
  # Disallow methods that allow anonymous authentication
  smtp_sasl_security_options = noanonymous
  # Location of sasl_passwd
  smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd
  # Enable STARTTLS encryption
  smtp_tls_security_level = encrypt
  # Location of CA certificates
  smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt

Restart postfix:

  systemctl restart postfix

Send test message:

  mutt -s "Test" user@gmail.com </dev/null