DMARC’s Subdomain Policy (sp) Tag
Keeping in mind that cybercriminals leverage unprotected subdomains for phishing exploits, it’s important to have a DMARC deployment plan for every subdomain you create, whether the parent domain DMARC policy is inherited, an sp= tag is published to rule the subdomains, or a p= tag is indicated for the subdomain.
DeploymentTechnical Guidance