[RESOLVED]
This thread:
Lead me to understand error was due to security setting aimed at blocking spoofed email
So recap when setting up Discourse with MIAB make the app.yml
## TODO: The mailserver this Discourse instance will use
DISCOURSE_SMTP_ADDRESS: box.server1.us # (mandatory)
DISCOURSE_SMTP_PORT: 587 # (optional)
DISCOURSE_SMTP_USER_NAME: discourse@server1.us # (optional)
DISCOURSE_SMTP_PASSWORD: woowooithides # (optional, WARNING the char '#' in pw can cause problems!)
DISCOURSE_SMTP_ENABLE_START_TLS: true # (optional, default true)
DISCOURSE_SMTP_AUTHENTICATION: "plain"
DISCOURSE_SMTP_OPENSSL_VERIFY_MODE: none
& change the notification email option in the admin panel required settings to match the MIAB account sending out the mail