Status 5.1.1#
smtp;550 5.1.1 <email@example>: Recipient address rejected: User unknown
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
Spam filter · 5.x.x permanent failure
Proofpoint SMTP 550 Errors: Every Bounce Response Explained
Every SMTP 550 response on record from Proofpoint, with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The mailbox is unavailable and the message is rejected for good. This is the catch-all permanent failure, covering everything from an unknown address to an authentication failure to a reputation block, so the wording after the number is what actually tells you the reason.
- Spam filter
- Proofpoint
- Code
- 550 (5xx)
- Responses
- 13
- Highest severity
- High
Proofpoint SMTP 550 responses
Status 5.1.1-2#
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
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
Status 5.1.1-3#
smtp;550 5.1.1 User Unknown
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
Status 5.1.1-4#
smtp;550 5.1.1 - This is not a valid email address. Please verify that you have the correct email address for your recipient.
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
smtp;550 5.1.8 <[email protected]>: Sender address rejected: Domain not found (in reply to RCPT TO command)
The receiver refused the message for good and points at an addressing problem (the recipient or sender address itself) (enhanced status 5.1.8). Use the wording above to pin down the exact fix.
smtp;550 5.1.8 Domain of sender address does not exist
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
smtp;550 5.5.2 <[email protected]>: Sender address rejected: need fully-qualified address (in reply to RCPT TO command)
The receiver refused the message for good and points at a protocol problem (a malformed or out-of-sequence SMTP command) (enhanced status 5.5.2). Use the wording above to pin down the exact fix.
smtp;550 5.7.0 Email rejected per sender's DMARC policy
The message did not pass the sending domain's DMARC policy, so the receiver rejected it. Sign the mail with DKIM for your From domain, or align SPF through a custom Return-Path, then send again.
Status 5.7.1#
smtp;550 5.7.1 <[email protected]>: Recipient address rejected: User email address is marked as invalid.
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
Status 5.7.1-2#
smtp;550 5.7.1 Relaying denied
The server will not relay mail for this destination. Send through the correct outbound server for the domain, and confirm the recipient really hosts mail with this provider.
Status 5.7.1-5#
smtp;550 5.7.1 Relay access denied
The server will not relay mail for this destination. Send through the correct outbound server for the domain, and confirm the recipient really hosts mail with this provider.
smtp;550 5.7.1 Service unavailable; client [x.xx.xx.xx] blocked using prs.proofpoint.com
The sending IP or domain is on a blocklist the receiver checks, so mail stays refused until the listing clears. Find which list flagged you, fix the underlying cause, then request removal. Delivery can stay blocked for up to a day after delisting while caches refresh.
Provider documentation
smtp;550 5.7.1 Service unavailable; client [x.xx.xx.xx] blocked using Cloudmark Sender Intelligence (Visit http://csi.cloudmark.com/reset-request/ if you feel this is in error)
The sending IP or domain is on a blocklist the receiver checks, so mail stays refused until the listing clears. Find which list flagged you, fix the underlying cause, then request removal. Delivery can stay blocked for up to a day after delisting while caches refresh.
Provider documentation
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
Proofpoint SMTP 550 questions
›What does an SMTP 550 error from Proofpoint mean?
The mailbox is unavailable and the message is rejected for good. This is the catch-all permanent failure, covering everything from an unknown address to an authentication failure to a reputation block, so the wording after the number is what actually tells you the reason. At Proofpoint, it is a permanent rejection, and the specific reason is in the enhanced status code and message text of each response below.
›How do I stop Proofpoint from returning SMTP 550?
Match your bounce text to one of the responses below and follow its guidance. Recipient-side wording means fix the address. Authentication or reputation wording (SPF, DKIM, DMARC, blocklist) means fix your sending setup, and check Proofpoint's postmaster documentation.