Email was designed without sender verification: anyone can claim to send on behalf of your domain. Attackers use this for phishing against your customers and employees. Three mechanisms close the gap.
The three building blocks
SPF (Sender Policy Framework): a DNS record lists the servers allowed to send for your domain.
DKIM (DomainKeys Identified Mail): your mail server signs outgoing messages; recipients check the signature using a public key in DNS.
DMARC: defines what recipients should do with messages that fail SPF or DKIM (none, quarantine, reject) and provides reports.
Rollout in steps
Collect all legitimate senders: mail server, newsletter service, ticket system, CRM.
Set up SPF and DKIM for every sender.
Start DMARC with policy "none" and reports.
Evaluate reports and fix misconfigurations.
Tighten gradually to "quarantine" and "reject".
SPF DKIM DMARCemail spoofingset up DMARCemail domain security
Frequently asked questions
What is DMARC for?
DMARC defines how recipients treat forged or unauthenticated emails from your domain and provides reports about them.
Do I need all three mechanisms?
Yes, they complement each other: SPF and DKIM authenticate, DMARC sets the rules and reporting.
Can DMARC block legitimate emails?
With wrong setup yes. That is why you start with "none", review reports and only then tighten.