Hilary – I heard Steve speak two years ago. Since then, I have been using ProtonMail. I use the free version. I tried the paid version and didn’t like it at all. It really is for very large companies and not a person with a single computer.
About the free version, you’ll need to use an email address like janedoe@protonmail.com. It’s in my email signature below my regular email address to remind clients and associates they have that option. (For secure email, use lynnplait@protonmail.com.)
When I get an email in my proton mail box, I get an email in my regular mail telling me so I don’t have to check PM all the time. I find it a cheap and easy solution to this problem since I’m not big enough to afford the portals like CPAs use. Good luck!