Email provider
ProtonMail SMTP Error Codes and Bounce Messages
Proton Mail is a Swiss provider and the largest host of end-to-end encrypted email.
- Codes on record
- 1
- Responses
- 1
SMTP 5501 response
A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 550 across every provider
ProtonMail bounce questions
›Why is ProtonMail bouncing my email?
Proton Mail is a Swiss provider and the largest host of end-to-end encrypted email. Match the exact wording of your bounce to one of the 1 responses on this page to find the specific reason and fix.
›How do I improve deliverability to ProtonMail?
Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes.
