What does SMTP error 550 5.5.5 mean and how do I fix it?

Key findings

• Policy rejection: The 550 5.5.5 error specifically signals that the email was rejected due to a strict recipient policy, such as a requirement for prior approval or whitelisting of the sender.
• Recipient-side issue: This error means the problem lies with the recipient's mail server configuration, not with your sending infrastructure or general email deliverability. For more on common 550 errors, see our article on what causes SMTP 550 errors.
• Rejected at DATA command: The error occurs after the DATA command, implying the server accepted the initial connection but rejected the message content or headers based on its internal policies. Learn more about how to find and interpret SMTP error codes.
• Permanent failure: As a 5xx class error, it signifies a permanent bounce, meaning the email will not be delivered without corrective action by the recipient. Some documentation also clarifies this, such as LeadConnector's bounce classification codes.

Key considerations

• Contact recipient directly: The most effective solution is to reach out to the recipient through an alternative communication channel (e.g., phone, another email address) and request that they add your sending domain or email address to their allow list.
• Verify whitelisting claims: If the recipient claims they have whitelisted you, the error indicates that the whitelisting is either incomplete, incorrectly configured, or not effective for the specific policy causing the 550 5.5.5 bounce.
• Review recipient's policies: Especially when sending to corporate or financial institutions, recipient servers often have extremely strict security and filtering policies. Understand that some organizations may only allow pre-approved correspondence.
• Address specific sender identity: When discussing whitelisting, clarify whether they need to allow the Envelope From address, the From header address, or your sending IP address.

Key opinions

• Frustration with false claims: Marketers frequently express frustration when clients assert that senders are whitelisted, yet 550 5.5.5 bounces persist, indicating a disconnect in understanding or implementation. This is a common aspect of why emails go to spam.
• Recipient control: The consensus among marketers is that the resolution lies entirely with the recipient, as the error points to a specific internal policy on their mail server.
• Difficulty of follow-up: Getting a recipient, especially a large organization, to adjust their email server settings can be a significant hurdle for marketers.
• Specific policy awareness: Marketers note that different 550 sub-codes, like 5.5.5 vs 5.1.1, point to distinct issues, requiring targeted troubleshooting. For more detail, see what causes 550 5.1.1 errors.

Key considerations

• Communicate action plan: Clearly explain to clients that the next steps involve contacting the recipient's IT team to adjust their server settings. As noted by Enginemailer, the 550 error typically means rejection by the recipient server.
• Provide context to recipients: When advising clients, suggest they provide the full diagnostic code (550 5.5.5 Message not delivered to user without prior approval) to the recipient's IT for faster diagnosis.
• Check email list hygiene: While this error isn't typically about a non-existent user, maintaining a clean email list with legitimate opt-ins can minimize such policy-based rejections in the long run.
• Explore temporary solutions: If urgent, marketers may inquire if a client can send to a personal email address or use an alternative contact method until the official work address issue is resolved.

Key opinions

• Strict pre-approval: Experts confirm that the error explicitly means the recipient's email address is configured to only accept mail from pre-approved senders, often seen with highly secure domains like banks.
• Recipient responsibility: The overwhelming expert opinion is that the fix for this error must come from the recipient's side. The sender cannot resolve it externally by simply changing their sending method or content. This differs from issues that might cause 550 relaying denied errors.
• Whitelisting confusion: While clients may claim they have whitelisted a sender, experts often find that the reported bounces indicate the whitelisting is not working as expected or is insufficient for the specific policy triggering the 550 5.5.5 error.
• Rejected after DATA: The fact that the rejection occurs in response to the DATA command means the server has received the full message content before rejecting it based on an internal policy. Understanding the SMTP transaction is key to email authentication and troubleshooting.

Key considerations

• Direct communication: Advise contacting the recipient via an alternative channel to request that they configure their email address to accept mail from the sender. As ScalaHosting notes, a 550 error implies the message was blocked.
• Identify sender details: It's important to clarify which sender address (e.g., Envelope From) needs to be on the recipient's allow list to bypass such policy rejections.
• Set clear expectations: Communicate to clients that the responsibility for resolution rests solely with the recipient, and the sender's options for external intervention are limited.
• Review list legitimacy: For sensitive recipients, question whether the email address was legitimately opted-in to the sending list, as unsolicited mail is more likely to trigger strict policies.

Key findings

• Permanent failure (5xx): RFCs classify 5xx SMTP reply codes as permanent negative completion replies, indicating that the mail transaction failed and the client should not retry without modification. This is distinct from soft bounces (4xx codes).
• Specific policy status (5.5.5): The enhanced status code 5.5.5 provides more detail beyond the generic 550, often relating to mail system capabilities or, as seen here, specific recipient policies requiring sender approval. For context, see LeadConnector's bounce classification codes.
• Rejection after DATA command: Documentation on SMTP protocol indicates that a 550 response to the DATA command means the rejection happened after the full message body was presented, suggesting a content or policy-based filter. For deeper insight into how RFCs define email behavior, check our article on what RFC 5322 says vs. what actually works.
• Recipient-specific interpretation: While RFCs provide general definitions, the precise human-readable message accompanying the 550 5.5.5 error can vary slightly between mail servers but generally conveys a policy rejection. This is similar to how email blacklists and blocklists are implemented.

Key considerations

• RFC compliance: While the issue is on the recipient's side, ensuring your own email sending practices (e.g., proper SPF, DKIM, DMARC alignment) are RFC-compliant can help build overall sender reputation, potentially reducing the likelihood of triggering overly strict recipient policies in the future.
• Log analysis: Documentation often stresses the importance of analyzing full SMTP logs to understand the exact point of rejection and the precise diagnostic code received, which can offer clues beyond the basic error message.
• Distinguish from other 550s: Recognize that 550 5.5.5 is distinct from other 550 errors, such as 550 5.1.1 (user unknown), each requiring a different diagnostic approach.
• Policy enforcement variations: Documentation implies that while the core meaning of 550 5.5.5 is consistent, the specific policies triggering it can vary greatly among different mail servers and organizations.