Change password on Postfix+Gmail relay setup

As root go to /etc/postfix.

Open main.cf.

Find the line smtp_sasl_password_maps to get the name of the file currently used.

Open that file and edit the password in it to the right of the ":" after the login/mail address.

Create a hash db file of the file: sudo postmap /etc/postfix/name-of-file-without-db-at-the-end

Restart postfix, service postfix restart.

Check /var/spool/deferred for any mail that was unable to be sent and the /var/spool/defer for the reasons.