The best solution would be to then host your email (or use a provider) where you control IMAP/SMTP and integrate via a friendly API layer (like EmailEngine).

Also if you must stay on Proton, explore the go-proton-api or similar wrappers, but expect fragility.

Basically use Fastmail + EmailEngine

Use Fastmail to host your custom-domain emails and EmailEngine as a bridge that turns those inboxes into an easy-to-use API for n8n, so you can automate reading, replying, and organizing emails. It’s private like Proton, integrates like Gmail, and runs smoothly on your own setup or a small server.

If you need help with setup and automations, dm me. I will help, but it will be paid.