I even did a stint where I self hosted email. It was fine, but gmail for some reason wants VERY specific security measures and kept rejecting my emails, even when others would go though on other platforms.

Ha, yes, been there, done that - it seems everything is working for now concerning confirmation sign-up mails for my Fediverse stuff like this Lemmy instance sent from my mail server, but, damn, was it a journey to get there.