ProtonMail offers encrypted contacts for both web and mobile applications (https://protonmail.com/blog/encrypted-contacts-manager/). Calendar and note functionality will be released in the future.
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I think there are people who would want to pay for a version where they only have some more space on top of the free version
They would not need the custom domain or 5 e-mail addresses.
I only use the pm.me (great idea) because it is shorter and I tend to see it as a shorter version of protonmail.com not as a secondary e-mail address.