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