ETA: I thought you meant how do I like the Proton mailbox@! :D

I like it. The only issue for me is that the search is slow, but that's because they have to compile all your data first...as opposed to Gmail, which already and always has access.

Another plus of Proton Mail is their masked email app. When I go to a site that asks me to enter an email, the app can create a masked email for me on the fly.

I don't do anything fancy, just use the light version with the email I made, and use anonaddy to alias for free. I use Thunderbird as a client.

It works, although the web app is kinda slow. If you enable MFA Tokens, instead of the password you made, you now type a PIN + TOTP code to login, which is dumb (They might be changing it soon). I know some have pointed out a security issue about flags or smth, specifically about how people can spoof your email and send messages as you. This comment specifically shows what tests failed and passed.

It's cheap (Light plan is ~1€ per month) and allows easy one click enabling of PGP for webmail and encrypted sending (to mailbox.org users) but if you're a pro you can do expert/customizable settings for those instead.

I just wanted something that was relatively private and secure, and will work with Thunderbird.

Maybe consider Posteo too, which has another lengthy post of Privacy.guides forums about whether it's good or not.

Honestly, maybe I would move to Posteo due to the DMARC policy and MFA being iffy on Mailbox, but we'll see. I use aliases to avoid too much spam anyway.