If your DMARC, SPF, or DKIM authentication is failing with a third-party mail service, check the following:
SPF: Ensure your SPF record includes the third-party service's mail servers. Only one SPF record should be present in DNS.
DKIM: Verify that DKIM signing is enabled in your third-party provider settings and that the correct DKIM key is published in DNS.
DMARC: Confirm that your DMARC record is correctly set up and not enforcing a strict policy that could block unauthenticated emails.
Domain Alignment: Ensure the "From" domain matches the SPF or DKIM domain to pass DMARC alignment.
Email Headers: Check the email headers for SPF, DKIM, and DMARC results to identify where authentication is failing.
Third-Party Service Settings: Some providers require additional configuration—check their documentation for DMARC compliance.