I'm dropping this here for my own future reference, and also to help anyone that's struggling with what an SMTP URI is when trying to configure the email extension in Google Firestore.

The URI Structure

What ended up working for me was:

smtp://[[email protected]]:[password]@[smtp hostname]

Gotchas

  1. I put in smtps instead of smtp - which didn't work for me
  2. I put in just the username, not including the domain, that also didn't work for me

Hope that helps you, or future Chris. :)