I’m looking to degoogle my spam-mails
I’ve been using Protonmail for a while now and it’s only gotten better.
I can only second Posteo. Using their services for years now, I can confirm that Posteo is caring about security, data protection and the environment (using green energy). Also you do not need to provide your mobile-phone number or personal information and you can use standard OTP apps to secure the weblogin when you want to use 2-Factor.
I am using several accounts shared between Thunderbird on Desktop and K-9 on Android.
The only issues I have is, when sending to some US providers that still do not have TLS (“Transportwegesicherung”) implemented. In this case I have to manually deactivate the “TLS-Versand-Garantie”-option in Posteo settings, before the email can be send. Happens twice a year or so.
Maybe the Posteo suggestion gets downvoted, because their mail services indeed cost money (instead of scanning your communication and selling your data). But I find 1€ per account per month a good deal for what you get.
Tutanota or protonmail
Proton Mail, Tutanota or Skiff should be good alternatives for you. Avoid any e-mail provider without EE2E and zero knowledge architecture.
I currently have an account on all three, but my daily is Skiff.
More important than e-mail provider to control spam is to use a unique e-mail address for each account you own. That could be attainable using e-mail aliases or e-mail forwarding services. Look up Simple Login, AnonAddy or even DuckDuckGo E-mail Protection for more information. Putting it simple, you create a different alias for each account. They all forward to your main e-mail inbox under different aliases. If needed, you can cancel the aliases thus ending spam from that origin.
I find it a very effective technique and my inbox is always pristine.
Would recommend mailbox.org or posteo.de.