Not mailbox.org (!) unlike many have suggested. In last few years mailbox has gone into the gutters in almost every aspect (almost) - I am stuck there because of a large recharge/purchase I had done and they don't do prorated refunds anymore.

There are other options - tuta, posteo, runbox etc (I have just made a longer comment and I am sure you can find more on the net).

IMHO - we should not ignore other things when looking for a service replacement I mean aspects of a service other than privacy and for me responsiveness and customer service comes near the top or at the top.