Hi Daniel 
you’d be glad to know it doesn’t the forum sends transactional emails by SMTP, so you need to log in to the SendGrid. Discourse can use any address in your subdomain.
Your telling discourse in the setting on the container you want discourse to always sent it’s transactional emails as noreply@ - account activation, email notifications, password reset emails, etc.
If i remember right, when i installed last year i needed to remove speech-marks in a key/password/address in the container. I wish i recorded exactly where, and the intresting errors i got before.