Comment by sandcat_

There's a difference between controlling the domain and self-hosting. You can still use Gmail and Outlook (I assume, I don't know for a fact) with a custom domain. But the difference is if any of those services become less reliable or whatever, you can move your email across to another provider. You can't do that if you're stuck on an @outlook.com address.

But also, even if you're self hosting on a server in your basement, you can still use SES to deliver your mail. Delivery is not an issue here.