Bounce error fix

Gmail 550 5.7.26: unauthenticated email blocked

Gmail refused your email because it couldn’t confirm it came from your domain. Here is how to get SPF, DKIM and DMARC passing.

What the bounce says

550-5.7.26 This mail has been blocked because the sender is unauthenticated. Gmail requires all senders to authenticate with either SPF or DKIM.

A second version mentions DMARC instead: “Unauthenticated email from yourdomain.com is not accepted due to domain’s DMARC policy.” Both mean the same thing: Gmail couldn’t confirm the email really came from your domain, so it refused it.

Why it happens

The service that sent the email isn’t in your SPF record.
DKIM isn’t switched on for that service, or the key isn’t published.
SPF and DKIM pass, but for a different domain from the one in your From address, so DMARC still fails.
Your SPF record breaks the 10-lookup limit, so SPF fails for everything.

How to fix it

Scan your domain. The full domain scan shows which of SPF, DKIM and DMARC fails.

Add the sending service to SPF. Use the SPF record generator to include it and count the lookups.

Switch on DKIM in that service. Follow the guide for Google Workspace or Microsoft 365, or the service’s own DKIM settings.

Match the From domain. The domain in your From address must match the domain that passes SPF or signs DKIM. Most sending tools call this “domain authentication”.

Check it worked

Run the scan again after you change your DNS, then send a test to a Gmail address.