Proton Mail

Free (IAPs) FROM proton.me NEEDS iOS 11 or later

If you want to get a better email experience that stops spam and trackers in their, well, tracks, then Proton

Mail is the app for you. Everything is encrypted by default on all your devices (not even Proton can access your mail), and the app doesn’t use your data for anything, including targeted ads. It’s your inbox, your way – isn’t that how email should be? The app (and service) is completely free to use, although Proton Plus (£49.99/year) and Proton Unlimited (£129.99/year) offer additional features.