Spam filter / gateway
Proofpoint SMTP Error Codes and Rejection Messages
Proofpoint is a corporate mail security gateway. Inbound mail passes through Proofpoint-owned servers before final delivery, recipients control their own allowlists and policy levels, and IP-level blocks are appealed through Proofpoint directly.
- Codes on record
- 3
- Responses
- 16
Postmaster & documentation
- https://help.proofpoint.com/Proofpoint_Essentials/Email_Security/User_Topics/040_spamsettings/041_adjustingyourspamsettings
- https://help.proofpoint.com/Proofpoint_Essentials/Email_Security/Administrator_Topics/110_logs/Common_Error_Codes_found_in_Message_Details
- https://help.proofpoint.com/Proofpoint_Essentials/Email_Security/Administrator_Topics/Other_Features/Proofpoint_Dynamic_Reputation_(PDR)_IP_blocklisting_and_IP_address_removal
SMTP 4212 responses
smtp;421 4.1.1 <[email protected]>: Recipient address rejected: unverified address: host example.com[x.xx.xx.xx] said: 450 4.1.1 <[email protected]>: Recipient address rejected: unverified address: lost connection with mail.example.com[x.xx.xx.xx] while sending RCPT TO (in reply to RCPT TO command)
smtp;421 4.1.1 <[email protected]>: Recipient address rejected: unverified address: Address verification in progress
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 421 across every provider
SMTP 55013 responses
smtp;550 5.1.1 <email@example>: Recipient address rejected: User unknown
smtp;550 5.1.1 <[email protected]>: Recipient address rejected: undeliverable address: host example.com[x.xx.xx.xx] said: 550 5.1.1 <[email protected]>: Recipient address rejected: user unknown
smtp;550 5.1.1 User Unknown
smtp;550 5.1.1 - This is not a valid email address. Please verify that you have the correct email address for your recipient.
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
SMTP 5541 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 554 across every provider
Proofpoint bounce questions
›Why is Proofpoint bouncing my email?
Proofpoint is a corporate mail security gateway. Inbound mail passes through Proofpoint-owned servers before final delivery, recipients control their own allowlists and policy levels, and IP-level blocks are appealed through Proofpoint directly. Match the exact wording of your bounce to one of the 16 responses on this page to find the specific reason and fix.
›How do I get past the Proofpoint spam filter?
Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes. Proofpoint also publishes postmaster guidance, linked on this page.
