SMTP 554 5.7.1 indicates a policy or reputation rejection, often for spam or prohibited content. Identify the rejecting system and reason code, then inspect authentication alignment, sending reputation, message content and relay behavior instead of repeatedly resending the same message.
Step-by-step checks
Read the complete NDR/SMTP diagnostic and identify the receiving filter, enhanced code, policy URL or reputation reference that made the decision.
Validate SPF, DKIM and DMARC alignment for the actual envelope/header domains and confirm the sending IP is authorized by the intended outbound path.
Compare a minimal plain-text test with the rejected message to isolate attachment, URL, wording or malformed-header factors without attempting to evade filtering.
Check sender/IP reputation and outbound message trace for compromise, unusual volume or relay configuration errors before requesting a delisting/review.
Useful verification commands
Use commands only on systems you administer and capture the read-only output before making a configuration change.
A controlled legitimate message must pass through the intended authenticated outbound path with SPF/DKIM/DMARC alignment and be accepted by the destination without policy rejection.
Evidence to keep
Keep complete NDR text, sending IP, SPF/DKIM/DMARC results, message trace, representative headers, reputation finding and any provider case/reference number.
Frequently asked question
Should I just change the message wording until it passes?
No. First determine whether the rejection is caused by authentication, reputation, compromise, policy or a specific legitimate content issue. Repeated blind retries can worsen reputation.