@Techaltar For a time I maintained my own carddav / caldav server for this, then I got lazy and setup a Google account to manage contacts and calendars, and only that (no mail, drive, etc.)

On my devices, I centralise my mails and calendars through local clients (Thunderbird / K9mail), which - like the contacts list on Android - are able to sync with the Google account. I don't use the web services.

This way, I can send a mail from my Outlook account to a contact saved in my Google account.

@Techaltar I gave them a shot but there is a *huge* caveat to their solution which should be made more clear : you can't sync their apps with the contacts list of your phone (due to encryption).

That's a deal breaker for me and I imagine many others. Can't manage 2 contacts list

That's interesting bc their commitment to encryption is of course commendable... but as is, it's either too much (bc it blocks usage), or not enough (the endgame of what they're trying to do here is... a new OS).