Gmail bounce "550 5.7.26 sender is unauthenticated": how to fix it

What's happening: Gmail rejected your message because it passed neither SPF nor DKIM for your From domain, or your domain's DMARC policy told Gmail to reject it. Since 2024 Gmail enforces this for everyone sending to personal Gmail addresses, and strictly for anyone sending 5,000+ a day.

How to fix it

  1. Check that your domain has exactly one SPF record (a TXT starting with v=spf1) and that it includes every service that sends as you, for example include:_spf.google.com for Google Workspace.
  2. Turn on DKIM for each sender. Google Workspace: Admin console → Apps → Gmail → Authenticate email → Generate new record, publish the TXT, then press Start authentication. Newsletter and CRM tools have their own DKIM setup page.
  3. Add a DMARC record if you have none: TXT at _dmarc.yourdomain.com with v=DMARC1; p=none; rua=mailto:you@yourdomain.com. Start at p=none and tighten only once reports show everything passes.
  4. Wait for DNS to update (usually minutes, up to a few hours), then send a test to a Gmail address and open Show original: SPF, DKIM and DMARC should all say PASS.

Not sure which record is wrong? Check your domain free: it shows which of SPF, DKIM and DMARC is failing, in 5 seconds, no signup.

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