Gmail 550 5.7.1: “This message is likely unsolicited email”

Short answer: Gmail's spam filter judged this message to be unwanted mail and refused it. It is about the message and how you send it (content, links, recipients who didn't ask, sudden volume), not one DNS record. Fix: send only to opted-in people, clean up links and content, and pass SPF, DKIM and DMARC.

The bounce looks like this
550-5.7.1 This message is likely unsolicited email. To reduce the amount of spam sent to Gmail, this message has been blocked.
550-5.7.1 [203.0.113.10] Gmail has detected that this message is likely unsolicited mail. … https://support.google.com/mail/?p=UnsolicitedMessageError
421-4.7.0 This message is suspicious due to the nature of the content or the links within. To best protect our users from spam, the message has been blocked.

What it means

Gmail's filter scored this particular message as spam and rejected it instead of delivering it to the spam folder. Google says it blocks only some mail that looks like spam, judging the wording, the links and the sender's history. Typical triggers: bulk or cold mail to people who never signed up, links to domains with a bad reputation, hidden text, a sudden jump in volume, or a forwarder passing spam along. The 421 4.7.0 “nature of the content or the links” variant points straight at the message body. If the bounce blames your domain or IP instead, see very low reputation; for “unusual rate of unsolicited email”, see 421 4.7.28.

How to fix it

  1. Send only to people who asked for your mail: confirm new sign-ups, never buy lists, and remove recipients who don't open.
  2. Check every link: it should be visible and easy to understand, and its domain must not be flagged as unsafe by Google Safe Browsing (transparencyreport.google.com/safe-browsing).
  3. Don't hide text with HTML or CSS, and don't mix promotions into receipts or other transactional mail.
  4. Check the domain below: SPF, DKIM with your own domain and DMARC should pass, and marketing mail needs one-click unsubscribe.
  5. Keep volume steady: raise it gradually, and send less while bounces continue.
  6. Watch the spam rate in Google Postmaster Tools and keep it under 0.3% (ideally under 0.1%).
  7. Forwarding mail into Gmail? Filter spam before it is forwarded: Gmail blocks forwarded spam and holds it against the forwarding domain (see forwarded email rejected).
  8. A 550 rejection is final, so nothing is retried. Resend the important messages once the cause is fixed.

Check your domain now

After the fix, send a test email to see SPF, DKIM and DMARC pass on a real message, then keep an eye on it: free DMARC monitoring shows every service that sends mail as your domain and which ones fail, in plain English.

Rather not touch DNS? I set up SPF, DKIM and DMARC without breaking your other senders, with a before/after report.

Get it fixed on Fiverr

Prefer to do it yourself? Get the step-by-step Fix Kit ($15) – 28-page guide, checklist, 20+ providers.

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