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’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.