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DMARC Subdomain Policy (sp=) — When You Need It
Most teams only set p=. Subdomains that send mail (mail.example.com) inherit policy context — but acquisitions and marketing sandboxes sometimes need different enforcement.
When to set sp=
Use sp= when a subdomain is less trusted or still warming up — quarantine there while root is reject. Document the decision — future you will not remember why.
Read DMARC policy and DMARC setup.
FAQ
What does sp= do?
Sets policy for subdomains separately from the organizational domain’s p=.
When is it needed?
When subdomains send mail with different risk — e.g. looser sandbox vs strict root.
Does the root DMARC apply to subdomains?
Often by inheritance — sp= overrides subdomain policy explicitly.
Is strict alignment related?
Separate — adkim/aspf control alignment strictness.
Example?
v=DMARC1; p=reject; sp=quarantine for stricter root than marketing subdomains.