Proton Mail

Proton Mail is a swiss-based email provider and the largest end-to-end encrypted email host.

Codes

550

550↑

550 5.7.1 Rejected by spam filter (in reply to end of DATA command)

Your email scored above the spam threshold and was rejected. Revise your email for any unwanted content prior to resending.

550 5.1.1 Recipient address rejected: Address does not exist

The email address does not exist. Check to make sure there are no typos or other mistakes with the address.