Preciso de ajuda/conselho sobre configuração de e-mail para uma instância Discourse auto-hospedada

[awesomerobot (Kris)]

@RyanO

in order for Mailjet to be able to send the noreply emails, do I have to create a noreply domain email address in an email hosting service? Like GSuite for example?

No you shouldn’t have to do that. There’s a walkthrough for mailjet over here: Howto use Mailjet as a free SMTP service for Discourse, have you completed all these steps?