[ancientsofmumu]

CTemplar as a service has no integration with standard protocols (SMTP, IMAP, CardDav, CalDav, etc.) even if you paid. It is/was a walled garden solution that can only be used with it's web portal or mobile client; when I was evaluating non-GMail solutions to de-Google it was an instant "nope" in my evaluations. It does not fit in the same category as other general purpose email solution providers.

[tasn]

Yeah, but it's the case with all of them. ProtonMail, Tutanota, etc, all of them are walled gardens that try to shove you into their proprietary lands.

I created EteSync[1] a contacts, calendars and tasks sync solution that's e2ee and privacy respecting but people kept on asking us to integrate with one of the above email solutions. Though they are all closed and don't interoperate. :(

[1] https://www.etesync.com

[RealStickman_]

Protonmail has a bridge for IMAP and SMTP for paying customers as well as an import/export tool.

I'm still moving my stuff to mailbox.org now though, I'm getting increasingly annoyed at having to use proton's mail app in addition to my main mail app.

[tasn]

But not for ProtonCalendar, and definitely not on Android.

Proton doesn't interact at all with the rest of the ecosystem. I'm not a Proton customer myself, I just hear it from our many customers that are frustrated by their closeness.

[Klonoar]

ProtonMail has plenty of escape hatches, I wouldn’t call them a walled garden.

[intc]

c1.fi (an email service yours truly is providing) supports SMTPS, IMAPS and ActiveSync. https://c1.fi/v/hn519/about?lang=en