Email Authentication: DKIM, SPF, and DMARC Explained

Email authentication is critical for email deliverability. Here is how the three main protocols work together.

SPF (Sender Policy Framework)

SPF validates that emails come from servers authorized to send for your domain.

Add a TXT record: v=spf1 include:_spf.yourmailprovider.com ~all

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to emails that verifies the sender and message integrity.

DMARC (Domain-based Message Authentication)

DMARC builds on SPF and DKIM to tell receiving servers what to do with failures.

DMARC policy options: none (monitor), quarantine (spam), reject (block).

How They Work Together

1. SPF verifies the sending server is authorized
2. DKIM verifies the message was not tampered with
3. DMARC ties them together and specifies enforcement

PostMTA provides automatic DKIM signing, SPF support, and DMARC reporting.

Learn more: https://postmta.com