DMARC (Domain-based Message Authentication, Reporting and Conformance) is a method that prevents spoofing. Spoofing is abuse of your domain as such that emails seem to originate from your domain. DMARC validates the email.

For more information, refer to these articles.

• Use DMARC to validate email from Microsoft
• DMARC: What is it and why do you need it?

Procedure

1. Open the MX Toolbox tool.
   
2. Paste the full email: the headers and the body.
3. Click Analyze Header.
4. Examine the results.