DMARC

DMARC tells receiving servers what to do with messages that fail SPF and DKIM checks, and can send you reports. It's a TXT record published at _dmarc on your domain.

Its policy has three levels: 'none' (monitor only), 'quarantine' (treat failures as spam) and 'reject' (refuse them).

Example: you add a DMARC record for yourbusiness.com with the policy set to 'none' and an address for reports. The reports show every service sending as your domain. Once all your real senders pass, you tighten the policy to quarantine, then reject, so impostors can't use your name.

Start with a monitoring policy and tighten it once you know all your legitimate senders. Jumping straight to 'reject' can block your own invoices or newsletters.

What it means for your price: DMARC is free, and large email providers now expect it from bulk senders. Some services sell tools to read DMARC reports, but a small business rarely needs one.

How to check yours: a free DMARC lookup shows whether your domain has a record and which policy it uses.