option to reject any email which is not encrypted
It would be great to add an opt-in setting to automatically bounce unencrypted incoming emails, with a polite auto-reply informing the sender that this inbox requires encryption.
For users who chose Proton specifically for privacy, receiving plaintext email is a risk, not just an annoyance. This would give power users full control over their security posture. No other mainstream provider offers this. It aligns directly with Proton's mission.
Martin7439
shared this idea
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thisismyusername
commented
I'm confused. How would this work in theory?
This could only be done by rejecting every non-Proton email, because there is no guarantee that anyone will encrypt their email with your public pgp key when sending from another server.
If they send a plaintext email, the only way to tell it's encrypted is when it arrives. For that you can create a Sieve filter to reject and send an auto-reply but at that point Proton's mail server already saw the message. If you store it, it will have zero-access encryption (encrypts with your public key after arrival). The only vulnerability is when it is in the server RAM momentarily.