Gmail SMTP delivery response
Understand Gmail 550 5.7.1: Delivery not authorized
The code alone is not a diagnosis: Gmail uses 550 5.7.1 for several unrelated permanent rejections.
A representative response is:
550 5.7.1 Delivery not authorized.
Do not repeatedly resend the same message. Correct the cause named in the full Gmail response first.
What this response means
Gmail uses 550 5.7.1 for several different permanent failures. The code by itself is not enough to choose a fix. Keep the complete response, including the sentence before the final - gsmtp.
Match the wording to the fix
- Policy prohibits this message: ask the sender or recipient domain administrator which rule blocked it.
- Invalid credentials for relay: correct the Workspace relay registration, SMTP authentication, envelope sender, or HELO identity named in the response.
- Likely unsolicited or low reputation: stop the affected traffic, check for compromise and complaints, then use Postmaster Tools before resuming slowly.
- IPv6 guidelines: configure valid forward-confirmed reverse DNS and passing authentication, or stop sending over that IPv6 address.
- Missing, duplicate, or malformed headers: fix the application so it emits one valid From field, a valid Message-ID, and RFC-compliant headers.
- IP not authorized for direct delivery: send through the SMTP relay provided by your mail service.
- Rate or relay limit exceeded: reduce traffic and wait for the applicable limit window.
Verify the repair
Send one controlled message through the same route and compare the new response or delivered headers. A clean public DNS check cannot prove that content, reputation, relay permissions, or message formatting is acceptable.
Related troubleshooting
If the full response explicitly names SPF, DKIM, DMARC, PTR, or a Gmail bulk-sender requirement, use the matching specialized guide instead of this general page.
Frequently asked questions
What does Gmail 550 5.7.1: Delivery not authorized mean?
It means Gmail permanently refused this delivery, but the exact reason is only in the text after the code; 550 5.7.1 is not one single problem.
Can MailFixIt prove this entire bounce from public DNS?
No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.
Related email diagnostics
Primary sources: Gmail SMTP errors and codes, Google email sender guidelines.