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Bounce error codes · Gmail and Google Workspace

Gmail 550 5.7.1: why your message was blocked

5.7.1 is Gmail's general “blocked by policy” code. The text after it is what tells you the cause: spam signals, a poor reputation, a malformed message or the recipient's own rules.

The exact error texts

  • Likely spam

    550 5.7.1 This message is likely unsolicited email. To reduce the amount of spam sent to Gmail, this message has been blocked. For more information, go to Why has Gmail blocked my messages?

  • IP reputation

    550 5.7.1 This message is likely suspicious due to the very low reputation of the sending IP address. To best protect our users from spam, the message has been blocked. For more information, go to Why has Gmail blocked my messages?

  • Domain reputation

    550 5.7.1 This message is likely suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked. For more information, go to Why has Gmail blocked my messages?

  • Recipient's policy

    550 5.7.1 The user or domain that you are sending to (or from) has a policy that prohibits the email that you sent. Contact your domain administrator for assistance. For more information, go to Sorry, a policy is in place that prevents your message from being sent.

Quoted from Google Workspace — Gmail SMTP errors and codes

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The versions of 5.7.1

Text mentionsCauseWhat to do
“likely unsolicited email”The message looks like spam to Gmail.Review content and recipients; see below.
“very low reputation of the sending IP address”Mail from that IP has a poor history.Shared IP: talk to your provider. Own IP: find the source of bad mail.
“very low reputation of the sending domain”Mail from your domain has a poor history, usually spam complaints.Postmaster Tools, list hygiene, slower volume.
“has a policy that prohibits the email”A Google Workspace admin's rule on the recipient's (or your own) side.Ask that admin. It isn't a deliverability problem.
“not RFC 5322 compliant”, “missing a valid Message-ID”, “multiple addresses in the From: header”The message itself is malformed.Fix the system that builds the message.
“IPv6 sending guidelines regarding PTR records”IPv6 sender without matching reverse DNS or authentication.See 550 5.7.25.

Fixing spam and reputation blocks

  1. Authenticate properly first. Reputation is tracked per domain and per IP, and authentication is how Gmail knows the mail is yours. Run the check above: SPF, DKIM with your own domain, DMARC.
  2. Look at your numbers. Verify your domain in Google Postmaster Tools. Google requires a user-reported spam rate below 0.3%.
  3. Clean up who you send to. Google's guidance: send only to people who opted in, confirm addresses, re-confirm periodically, and consider unsubscribing people who never open. Never buy lists.
  4. Make leaving easy. A clear unsubscribe link, and one-click unsubscribe for bulk marketing mail.
  5. Slow down. After a block, send smaller volumes to your most engaged recipients and increase gradually.

If the bounce names your IP, the blacklist checker shows whether it's also on public blocklists. Google tells shared-IP users to make sure the IP isn't on any blocklist.

Fixing header and format blocks

Google requires messages to follow RFC 5322. The 5.7.1 versions about headers usually come from custom scripts or misconfigured apps:

  • Exactly one From header with one valid address, on a valid domain.
  • A unique, valid Message-ID on every message.
  • No duplicate headers, and no unencoded non-ASCII characters in headers.

Questions

Why does Gmail use one code for so many problems?

5.7.1 is the generic “delivery not authorised” code in the security or policy class. Gmail adds the specific reason in the text, so always read the full line.

How long does a low reputation last?

Google doesn't publish a duration. Reputation follows what recipients do with your mail, so it improves as complaint rates drop and engagement rises. Watch it in Postmaster Tools.

Can I ask Google to unblock me?

Fix the cause first. Gmail's bounce text points to its sender guidelines, and Postmaster Tools shows whether your reputation and spam rate are improving.

Does 5.7.1 from Microsoft mean the same thing?

No. Enhanced status details are each provider's own. Microsoft 365 uses 5.7.1 for different situations, so look up the provider that sent the bounce.

Sources

Last reviewed: