Gmail 550 5.7.1: “very low reputation of the sending domain” (or IP)

Short answer: Gmail blocked the message because your sending domain (or IP) has a very low reputation with Gmail, usually after spam complaints or past spam. Passing SPF and DKIM doesn't override it. Fix: stop the source, keep the spam rate in Postmaster Tools under 0.3%, clean your list and ramp up slowly.

The bounce looks like this
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.
550-5.7.1 [203.0.113.10] Gmail has detected that this message is likely suspicious due to the very low reputation of the sending IP address. …
421-4.7.0 This message is suspicious due to the very low reputation of the sending IP address. To protect our users from spam, email sent from your IP address has been temporarily rate limited.
550 5.7.350 Remote server returned message detected as spam -> 550 5.7.1 … very low reputation of the sending domain …

What it means

Gmail keeps a reputation for every sending domain and IP, built from how its users treat your mail: spam reports, mail to people who never signed up, and spam sent in the past (often from a hacked mailbox or website form). At “very low”, Gmail blocks some of your messages outright, even when SPF, DKIM and DMARC pass. The wording says what is at fault: sending domain (your domain's own history, which follows you to any server) or sending IP address (the server or shared pool you send through). 421 4.7.0 is the temporary version, and your server retries. Microsoft 365 and Outlook.com senders see the same text inside 550 5.7.350 Remote server returned message detected as spam. If Gmail objects to the message itself instead, see “likely unsolicited email”.

How to fix it

  1. Find and stop the source first: a hacked mailbox, website form or script sending spam, or a campaign to a bought or old list. Pause bulk sends until it's fixed.
  2. Check the domain below: SPF, DKIM (signed with your own domain) and DMARC must pass. That alone won't lift the block, but Google gives no help to senders who miss its requirements.
  3. Set up Google Postmaster Tools (postmaster.google.com) for your domain and keep the user-reported spam rate below 0.3%; Google recommends under 0.1%. Watch the spam rate and compliance status: Google is retiring the old domain and IP reputation charts.
  4. Mail only people who opted in: confirm new sign-ups, never buy lists, and remove recipients who don't open your mail.
  5. Give marketing mail one-click unsubscribe (List-Unsubscribe and List-Unsubscribe-Post headers) and honour unsubscribes within 48 hours.
  6. Restart slowly: send to your most engaged recipients first, keep the daily volume steady and raise it gradually. If bounces continue, send less until they stop.
  7. IP variant: on a shared IP (newsletter tool, hosting provider), ask the provider about its sending pool; on your own server, check blocklists and reverse DNS (see 5.7.25).
  8. There is no form to remove a reputation block; it recovers as Gmail sees clean mail. Once you meet every requirement (bulk senders: spam rate under 0.3% for 7 days in a row), use Report delivery issue in Postmaster Tools.

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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