Start at p=none in monitor mode: one TXT record tells you who is sending as you, and it cannot reject a single legitimate message.
The full path to a live, safe DMARC policy. Each crumb is a real step in the Directions below.
DMARC checks that SPF or DKIM passes and aligns with the From: domain. If neither is set up, a strict DMARC policy will reject your own legitimate mail. Make sure both are live before you publish anything stricter than monitoring.
Go to the DNS zone for your domain at your registrar or DNS provider. You are adding exactly one TXT record at the special host _dmarc.
Set the host/name to _dmarc (your panel turns it into _dmarc.example.com). Use p=none so nothing is rejected, and point rua at a mailbox you actually read so reports arrive.
Host: _dmarc Type: TXT Value: v=DMARC1; p=none; rua=mailto:dmarc@example.com; fo=1
Within a day or two you will receive zipped XML aggregate reports from mailbox providers. Drop them into a free DMARC report reader to see every source sending as your domain — including shadow IT and spoofers.
Confirm every legitimate sender (your mail host, SendGrid, your CRM, invoicing tools) is passing and aligned before you tighten anything.
Once the reports show only known senders passing, step the policy up: first p=quarantine, optionally with pct=25 to ramp gradually, then p=reject. Reject is the only setting that actually stops spoofing.
v=DMARC1; p=reject; rua=mailto:dmarc@example.com; adkim=s; aspf=s
No reports are arriving.
Confirm the rua mailbox exists and can receive external mail, and that the record is at _dmarc, not the root. Some providers also need the rua domain to authorize external reporting with a _report._dmarc record.
Legitimate mail started getting quarantined.
A sender is passing SPF/DKIM but not aligning with your From: domain. Move back to p=none, fix alignment for that sender, then re-tighten.
Two DMARC records exist.
Only one TXT at _dmarc is allowed; multiple records make the policy void. Merge into a single record.
Strict alignment broke a vendor.
adkim=s/aspf=s require exact-domain alignment. If a vendor sends from a subdomain, relax to relaxed (the default) or onboard them onto a subdomain you control.
Written and maintained by Ben McDaniel. Drafted with AI assistance and human-reviewed against each vendor's current setup flow. Vendor interfaces change — if a step looks different, the underlying record is what matters.