Passwords I would recommend Bitwarden or KeePass (both of which are in the PrivacyGuides wiki, particularly usefull for KeePass where there are different clients depending on OS)

Email / contacts / calendar I am still struggling on to be quite honest. I am debating right now on Mailbox.org + EteSync OR just using Posteo.de (while it has some security regressions compared to Mailbox.org, it has encrypted contacts and calendar). To be quite honest though the options available in this space are quite frustrating, it is really hard to find a solution that allows for interoperability / data portability as well as E2EE / elevated security.

I would say the only potential “benefit” is if the account contains non-public facing personal information - you are reducing the chance it gets leaked via data breach (assuming, of course, they actually erase your data properly)

But I would say it is at least worth it to reduce that potential risk, but you should also go into it assuming that anything that was publicly accessible has been archived / saved by someone.

I for some reason recall at one point WhatsApp’s encryption was actually an audited implementation of Signal’s encryption. But that is so long ago that I doubt that holds much weight now ¯\_(ツ)_/¯

Would it run ok on a SBC, such as a raspberry pi? I don’t mind self hosting, but I don’t have the space for a full blown server setup in my appartment sadly (as fun as it would be)

I see in the FAQ they mention that “If you would like, you can encrypt your calendar and address book with your password. Therefore, only you have access to your data” (translated by myself into English, sorry if it isn’t exact)

Is there any “downsides” to this in terms of interoperability with other calendar / contact apps?

Thank you so much for your suggestion, this seems like it fills the issues I had when researching mailbox.org

How reliable is the syncing? I currently sync a lot of things with Syncthing, and while it is great to not rely on a shady centralized cloud service, decentralized syncing also has its own problems (potential sync conflicts in my KeePass databases mostly)

It definitely seems like an interesting option though! Thank you so much :)