I’m not sure if mailbox encrypts their calendar and contacts. I know tuta and Proton do but I self host that stuff anyway so I don’t care.
I use to selfhost everything, including email. However, emailing anyone from my domain I was 99% of the time in the spam list if it went though at all. I got fed up and paid someone to do it for me.
My understanding is only tuta to tuta is e2ee (via GPG). However, When you send or receive an external (non-tutanota)email, all they do is encrypt it for your inbox. Obviously its stored unencrypted in gmails servers, if you’re talking to someone at gmail, for example.
From what I remember, you can’t even use GPG to encrypt an email to someone external, you have to use their service that someone has to click a link, put in a password to view.
As for e2ee on the wire, almost all emails are encrypted, this isn’t unique to tuta. It’s basically HTTPS but for emails. Only a bad or misconfigured host would be unencrypted/HTTP.
Edit: to answer your question more directly, i believe mailbox.org + GPG encrypted inbox is the exact same thing as tuta. Not exactly E2EE but I get IMAP and I can use Thunderbird and use GPG with external people.
I use to use tuta as my provider but the lack of IMAP support I moved to mailbox.org basically the same thing if you give them your public GPG key for them to encrypt your inbound emails.
Wasn’t startpage sold to a advertising company?