Protonmail has your private keys😃

And...

Due to limitations of the SMTP protocol, we have access to the following email metadata: sender and recipient email addresses, the IP address incoming messages originated from, attachment name, message subject, and message sent and received times. We do NOT have access to encrypted message content, but unencrypted messages sent from external providers to your Account, or from Proton Mail to external unencrypted email services, are scanned for spam and viruses to pursue the legitimate interest of protecting the integrity of our Services and users. Such inbound messages are scanned for spam in memory, and then encrypted and written to disk.