To be fair to Proton, it’s not necessarily them who’s blocking your emails. In my case, I’m able to send emails to fx. an @hotmail.com address, but not other domains. And from the error messages I get (though I don’t use Proton), it looks like it’s the receiving mail server that’s blocking my incoming mail, not my own server blocking my outgoing mails.
Thanks for replying, I ended up with Simply.com, a Danish provider (I live in Denmark). They didn’t want any KYC besides the usual you give when paying with a credit card, full name, address, email, phone. It’s a .me domain, so maybe that’s why.
My domain is still being transferred, so I’m crossing my fingers, but it’s a quite big provider, so I’m not really worried.
May I ask what domain registrar you switched to? I’m having the exact same issue, albeit not with Proton but another email provider.
Joplin synced to a self-hosted sync server with E2EE on, that’s my setup. Works great.