You should be fine on the big providers. There's a weird horseshoe situation where anti-Google doomposting looks a lot like pro-Google FUD that I think leads people to believe only Google and maybe Microsoft are capable of sending mail any more.

Something like mailbox.org should be fine. Even a carefully-chosen VPS running your own email server should be fine (works for me, no delivery problems in ~2 years)

Tell me you haven't run a large email server without telling me.

There's a reason even large corporates that can easily afford the resources to run email their email themselves decide against it.

There are a handful of good providers, not just Google and Microsoft, but the two hyperscalers do have very good offerings, so of course they have a lot of the market.

You're right, I run a small email server. I told you.