I'm intrigued to try to understand whether this organisation's email services are symmetrically secure under all use conditions :
(their own website is : https://protonmail.com/
I see the security when both ends are using their service, but what would be the situation when one of them is using Outlook or GMail, or another platform ?
I assume that (apart from trusting their bona fides per se as presented on their website blurb) they a) at least can see / monitor session meta data, and b) almost without doubt have master access to all the accounts they run, and could thus easily view emails in clear text if they chose.
Any enlightened comment on this very welcome. ; )