Mailbox.ORG https://www.privacyguides.org/en/email/

I use Proton and it has this bridge application where it connects to the Proton servers and then serves your mail to Thunderbird or whatever locally. So that might work for you, but I'm not sure.

Posteo is pretty great

Fastmail.com https://www.fastmail.com/

Take a look at Migadu. Maybe that fits your criteria. I moved there from Tuta.

The FSF has a page with recommended mail services Free Software Webmail Systems

Riseup.net.

I am currently hosting my own email on a server that I rent and I am absolutely sick and tired of email issues, spam, google randomly being assholes and blocking my family's traffic, just stupid shit. It's a second fucking job at times. I have DKIM, DMARC, SPF all configured correctly, Google just randomly decides to stop my traffic randomly. Which of these options would you recommend for say up to 20 email accounts or so, using your own domain? I assume all of these options do things like spam filtering on the back end.

To be clear, I am not looking for free, just reasonable.

For privacy specifically take a look at https://www.privacyguides.org/en/email/ .

For just a paid provider where you are the customer not the product, consider FastMail or a hosting offering such as NameCheap. By hosting I mean the one that is part of their hosting plans not their email specific offering though that is interesting also but quite expensive.

I have been using Disroot Mail since August. It's a nice mail provider focused on not harvesting/selling your data.

iCloud