This has been a key feature in my decision to settle on a primary email provider. With ProtonMail and Tutanota without a true suite of personal organization, I settled on FastMail with the leery eye that it may includes some compromises on privacy. ProtonMail is soon to be releasing their calendar product, though their pricing is a few times more than Tutanota.

Edit: This might be against protocol (I'll delete if so) but I did some further digging

- Why is Protonmail better than Tutanota : https://www.reddit.com/r/ProtonMail/comments/b84kd3/why_is_p...

- And, why is Tutanota better than Protonmail: https://www.reddit.com/r/tutanota/comments/b82a05/why_is_tut...

Very interesting.