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Gmail

550 5.7.27 “Gmail requires bulk email senders to authenticate”

Senders of about 5,000 or more messages a day to personal Gmail accounts must pass both SPF (5.7.27) and DKIM (5.7.30), not just one of them. The 421 versions slow your mail down instead of rejecting it.

Codes: 550 5.7.27 or 550 5.7.30. Source: Google Workspace: Gmail SMTP errors and codes.

What usually causes it

  • SPF for the bounce (envelope) domain doesn't cover your email service.
  • DKIM signing isn't turned on, or the published key doesn't match after a key change.
  • A gateway or footer changes the message after it was signed.

How to fix it

  • Do both fixes from the 5.7.26 page: one complete SPF record, and DKIM signing in every service.
  • For Microsoft 365, publish the selector1 and selector2 _domainkey CNAME records, then enable DKIM.
The free email check can find part of this

The free check finds SPF errors, the lookup limit and published DKIM keys. It can't see whether your mail was actually signed.

Run the free email check

Want it fixed? Our email deliverability packages start at $49 for an audit and plan. Other error codes.