How to Fix 550 5.7.1 Blocked Errors
A 550 5.7.1 is a hard rejection — the provider refused your mail outright. Unlike a 421, this needs immediate attention. Here's the fix.
TL;DR
550 5.7.1 is a permanent block, usually from poor reputation, a blacklist listing, or failed authentication. Identify which, fix the root cause, then resume carefully.
What 550 5.7.1 means
The leading 5 means permanent failure. 5.7.1 is a policy rejection — the provider is actively blocking your mail, not just deferring it. This is more serious than a 421 throttle.
Common causes
- Blacklisted IP/domain — check and delist.
- Failed authentication — SPF/DKIM/DMARC misconfigured.
- Poor reputation from complaints or spam-trap hits.
- Missing rDNS or policy violation.
How to diagnose
Read the full SMTP response — providers often include a URL or reason. Then check reputation and blacklist status to pinpoint the cause.
How to fix it
- Blacklist? Fix the cause and request delisting.
- Auth failing? Repair SPF/DKIM/DMARC and rDNS.
- Reputation? Clean your list, cut complaints, and rebuild slowly.
After fixing
Don't resume full volume immediately — ramp back like a warmup while monitoring closely.
AutoPMTA flags auth, rDNS and blacklist issues that cause 550 blocks — before they happen. See pricing.
Key takeaways
- 550 5.7.1 is a permanent policy block, not a deferral.
- Usual causes: blacklist, failed auth, poor reputation.
- Read the full SMTP response to diagnose.
- Fix the root cause, then ramp back gradually.
Frequently asked questions
What does 550 5.7.1 mean?+
It's a permanent SMTP rejection on policy grounds — the provider is blocking your mail. Common reasons are blacklisting, failed SPF/DKIM/DMARC authentication, or poor sender reputation.
How is 550 different from 421?+
A 421 is a temporary deferral (your mail will be retried), while a 550 is a permanent rejection that needs you to fix the underlying cause before mail will be accepted.
How do I fix a 550 5.7.1 block?+
Diagnose the cause from the SMTP response, then act: request delisting if blacklisted, repair authentication and rDNS if failing, or clean your list and rebuild reputation if that's the issue.