thanks that got me back on track informational wise 
I would suggest to extend the comment by saying that this email can be changed after the installation by going to {discourse-domain/admin/site_settings/category/required
(but saying that the SMTP log- in can only be changed by a rebuild, they are read-only in the settings).
How to configure Mailgun Email Server on Discourse Forum correct way? - Detailed and Verified Steps • Crunchify is illustrating the relationships not too bad.
I don’t mind doing the PR, if it could be accepted as an improvement.
I find some good guides for the telnet work, explaining it well what has to be done when TLS is used (second covers Zoho Mail, what I currently use).
and good explanation for What is the difference between the HELO/EHLO commands? | RedinSkala