WHOOO HOOOOO! It’s working!! (Self signed)
Some things to note:
- In the code in the post above (15) the certificate has to be named .crt (and not .cert!)
- The hostname when creating the self signed cert should not have ‘www’ in it.
- The pop3 polling host in the Discourse control panel should just have the hostname (so not mail.domain.com, just domain.com).
I do have other problems tho 
RateLimiter::LimitExceeded but at least we’ve moved on a bit!
Hope this thread proves useful for others too 