If you have discourse setup and running, and decide you want to receive email on discourse, you’ll need to get an api from SendGrid. However, i got my api from MailGun.
This api means there’s never really any inboxes. Mod/Admin can set any inbound email address for a group/category, given that the address domain matches what the trans email provider allows.
Through the api, the System can take steps to ensure that email is delivered to a topic. If this fails internally, the email trace stays on the admin panel logs. Oftentimes, if System cannot create staged user for inbound email, the mail provider of the sender will send an Undeliverable - with text including “do you have an account here?”. This is what i’ve experienced.