I can see your concern about messages via email, but I know for me personally, email is just not a thing anymore. Forgetting plain SPAM, corporations/marketing/etc have ruined email into this signal that has such a low S/N ratio that it's just not useful. What percentage of internet users actually use email for communication anymore? Sure, some, but it's not my largest attack vector (I consider Google/FB as attacking me).

Anything serious goes trough emails and this is the data I’d be most worried about leaking - anything from security related stuff like login/id confirmation to receipts, confirmations, sensitive data, professional communication.

Waaay more valuable than FB scraping my phonebook and photos

This may be true for personal communication but any sort of business deal is going to be happening over email. Mortgages, selling your company, large sales... All of the contracts are going to end up in your inbox.