Part 1: Authentication Fundamentals
Critical Foundation
Email authentication is non-negotiable in 2025. Without proper SPF, DKIM, and DMARC setup, your emails will likely land in spam or be rejected entirely by major providers.
Understanding SPF Records
SPF (Sender Policy Framework) tells receiving servers which IP addresses are authorized to send email on behalf of your domain. It's your first line of defense against spoofing.
v=spf1 include:_spf.google.com include:sendgrid.net ip4:192.168.1.1 ~allThis record authorizes Google Workspace, SendGrid, and a specific IP to send emails.
Implementing DKIM Signing
DKIM (DomainKeys Identified Mail) adds a digital signature to your emails, proving they haven't been tampered with in transit and genuinely come from your domain.
Generate DKIM Keys
Use 2048-bit keys for better security. Most ESPs handle this automatically.
Add DNS Records
Publish public key in DNS as TXT record at selector._domainkey.yourdomain.com
Enable Signing
Configure your email service to sign outgoing messages with private key.
Setting up DMARC Policies
DMARC (Domain-based Message Authentication, Reporting & Conformance) ties SPF and DKIM together, telling receivers what to do with emails that fail authentication.
DMARC Deployment Strategy
- Start with p=none to monitor without affecting delivery
- Analyze reports for 2-4 weeks to identify legitimate senders
- Move to p=quarantine once you've authorized all senders
- Finally implement p=reject for maximum protection
Test Your Deliverability Setup
Use our free spam score checker to verify your authentication is properly configured.
This is a preview of the full guide.