Gmail "550 5.7.1 Our system has detected that this message is likely unsolicited mail": what to do

What's happening: Gmail blocked the message based on its spam judgement: sender reputation, user complaints, content and authentication together. Authentication alone won't override a bad reputation, but missing or failing SPF, DKIM or DMARC makes Gmail far less forgiving, so it's the first thing to rule out.

How to fix it

  1. Check that SPF, DKIM and DMARC all pass and align with your From domain (the free checker below shows this in seconds).
  2. Sign up for Google Postmaster Tools for your domain to see your domain reputation and spam complaint rate. Gmail wants complaints under 0.3%, ideally under 0.1%.
  3. Stop sending to old, bought or scraped lists, remove addresses that bounce, and add a one-click unsubscribe (List-Unsubscribe header) to bulk mail.
  4. Avoid sudden volume jumps: if you were blocked after a big send, drop back and ramp up gradually to engaged recipients first.
  5. Strip link shorteners and lots of links or images from the message, and make sure every link domain is your own or reputable.

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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