Hi there. Welcome.
You can try any of these: https://github.com/discourse/discourse/blob/master/docs/INSTALL-email.md
I’m testing Mailjet and is working very good for the moment. You can chose domains or accounts, their have a free plan that covers the basis (and more that another providers offers).
If you want to recieve mails, you can check that: Direct-delivery incoming email for self-hosted sites or try with another provider because Mailjet don’t work as reciever.