For that use case you can just use a temporary email provider like temp-mail.org which are harder to blacklist since they have a lot of random domains.

Firefox Relay seems easier to use, thanks to the one-click generated emails by the browser extension and the fact that the emails arrive in your actual inbox. But I agree that the domain is going to land on all the blacklists -- I hope they implement alternative domains for this reason.

Yep I often use "ten minute mail" for this too.