What DMARC is, why a small business needs it, and the one line to add to your domain to start.
The problem it solves
- Anyone can send an email that claims to come from your address. Fake invoices sent to your customers “from” you are a common fraud.
- DMARC is a setting on your domain that tells receiving mail servers what to do with emails that claim to be from you but are not.
The three records that work together
- SPF lists the servers allowed to send email for your domain.
- DKIM adds a signature to your outgoing email that proves it was not changed.
- DMARC tells the world what to do when an email fails those checks, and asks for reports so you can see who is sending as you.
Your email provider (Google Workspace, Microsoft 365 or your host) gives you the SPF and DKIM values. DMARC you add yourself.
How to start safely
Add a TXT record named _dmarc at your domain registrar or DNS provider, with this value, using an address you read:
v=DMARC1; p=none; rua=mailto:you@yourbusiness.ie- “p=none” only watches and reports; it blocks nothing, so it cannot break your email.
- After a few weeks of reports showing your real email passes, change it to p=quarantine, then p=reject. That is when the protection starts.
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