Email Deliverability 101: SPF, DKIM, DMARC Explained

A plain-English guide to email authentication protocols and why they matter for cold outreach.

Why Email Authentication Determines Cold Email Success

Without proper authentication, your cold emails will land in spam regardless of how good your copy is.

SPF (Sender Policy Framework)

A DNS TXT record that lists which mail servers are authorized to send email on behalf of your domain.

DKIM (DomainKeys Identified Mail)

Adds a cryptographic digital signature to every email. Proves the email was sent by an authorized system and not altered in transit.

DMARC

Ties SPF and DKIM together and tells receiving servers what to do when authentication fails.

The Alignment Problem

The most common deliverability failure is DMARC alignment failure caused by shared SMTP infrastructure. This is why dedicated Google Workspace and Outlook 365 inboxes fundamentally outperform shared SMTP.