Going back to a dumb phone soon, would make the transition easier if there was an app for Kindle fire tablet
The ability to manually block an email would be great. I disagree in automatically blocking all emails from Gmail, Yahoo, etc. This would just limit greatly the usefulness of protonmail. If one couldn't receive any email from Gmail I would be force to stop using protonmail
I use protonmail for almost all of my communications (still have Gmail to track the last emails down and change them) an integrated calendar ability would make protonmail a lot more handy for users.
Please make a Calendar app. This would benefit because it would help people move farther away from the Google ecosystem.