The 550 5.7.1 SMTP error means the receiving server rejected your email due to a policy rule — blocklist, authentication failure, or content filter. Learn how to diagnose and fix it.
5.7.1
| Component | Value | Meaning |
|---|---|---|
| Class | 5 | Permanent failure |
| Subject | 7 | Security or policy |
| Detail | 1 | Message Rejected by Policy |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
The receiving server rejected your email based on a policy rule. This broad code can mean your IP is blocked, authentication failed, or content triggered a spam filter.
Google uses 5.7.1 for both blocklist and policy rejections. Check your IP and domain reputation in Google Postmaster Tools.
📖 Google Workspace / Gmail documentation →Microsoft 365 returns 5.7.1 when the sender IP or domain reputation is poor. Check with Microsoft SNDS.
📖 Microsoft 365 / Outlook documentation →These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
550 5.7.1 [198.51.100.42] The IP you're using to send mail is not authorized to send email directly to our servers. 550 5.7.1 Message rejected due to content restrictions
Fixing this type of bounce requires correctly configured SPF, DKIM, and DMARC records. Our free Domain Checker analyses all three in one scan and tells you exactly what to fix.
Run a Free Domain Authentication Check →Paste your full NDR email, SMTP error line, or mail log fragment to get an instant plain-English diagnosis.
Open the Bounce Decoder →