550 Rejected by Header Based Anti-spoofing Policy


Issue in delivering Marketo Email (especially for mimecast users). Email get bounced with Error: 550 Rejected by header based Anti-Spoofing policy


This error can happen if:
  • You have not properly white listed the Marketo IPs
  • You have an issue with DKIM/SPF set up and configuration

Please whitelist the set of Marketo IPs found in the doc below and make sure SPF and DKIM are set up correctly for your email domain