Data Nexus

Security

Three DNS records that together decide whether anyone can send mail pretending to be your domain — and whether your own mail reaches the inbox.

Formula

SPF: which servers may send · DKIM: a signature proving the message was not altered · DMARC: what to do when either fails

SPF
a TXT record listing the servers authorised to send for the domain

DKIM
a public key in DNS against which each message is signed

DMARC
a policy — none, quarantine or reject — plus an address for the reports

DMARC without SPF and DKIM aligned to the visible From domain does nothing. Alignment is the part usually missed: a message can pass SPF for the sending service's own domain while the From header says yours.

01/What it means

Without an enforcing DMARC policy anyone can send invoices, password resets and instructions to your staff and customers from an address that looks exactly like yours. This is not a theoretical risk; it is the standard opening move of an invoice-redirection fraud.

The rollout has one correct order and skipping it breaks legitimate mail. Publish SPF and DKIM; publish DMARC at p=none with reports going somewhere a person reads; spend a few weeks finding every legitimate sender — the CRM, the invoicing tool, the newsletter, the booking system — and authorise each; then move to quarantine, then to reject.

02/What people get wrong

Monitoring mode is not protection. It reports impersonation without stopping any of it, and because nothing visibly breaks, it survives indefinitely. It is a stage in a migration, not a configuration.

Next

The definitions are the easy part. Whether the figure on your dashboard was computed this way is a different question, and usually the more expensive one.