Tools
Getting DMARC to enforcement without breaking your mail
Almost every domain publishes a DMARC record at p=none and stops. The path to reject, and the two sources of legitimate mail that always break it.
Microsoft
p=none protects nobody
A DMARC record at p=none tells receiving servers to do nothing differently and send you reports. It is the correct starting point and a terrible finishing point, yet an enormous share of domains have been sitting there for years believing they have DMARC.
Only p=quarantine or p=reject actually stops somebody sending mail as your domain. Everything before that is measurement.
The path that works
Publish p=none and collect reports for a month
You are looking for every legitimate source of mail using your domain. A month catches monthly billing runs, which a fortnight misses.
Fix alignment, not just authentication
SPF passing is not enough. The domain that passes must align with the From domain. This is the single most common reason a source fails DMARC while its owner insists it is configured.
Move to p=quarantine with a percentage
Start at pct=10 and raise it. A percentage rollout turns a potential mail outage into a slow trickle of reports you can act on.
Go to p=reject once the reports are clean
Not before. And keep reading the reports afterwards, because a new marketing platform will be onboarded without telling you.
The two things that always break
Marketing platforms, because somebody signed up without involving IT and the sending domain does not align. And mailing lists or forwarders, which rewrite messages in transit and break DKIM signatures by design.
Both are solvable. Neither is discovered until you look at reports, which is why the reporting month is not optional.
The verdict
Get to p=reject, with a percentage rollout
It is free, it stops direct domain spoofing outright, and increasingly it is a precondition for reliable delivery to large mailbox providers.
Do not jump straight to p=reject on a domain you have not measured. That is how payroll notifications disappear on a Friday.
Disclosure. Some links on this site are affiliate links. Scoring weights are published before any programme is joined, and commission is never a ranking input. Full policy, and the method behind this guide.