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.
Puzzle Inbox configures SPF, DKIM, and DMARC automatically for every inbox. No DNS expertise required.
Related Reading
- How to Set Up SPF, DKIM, and DMARC for Cold Email in 2026 — A complete step-by-step guide to configuring email authentication records that ensure your cold emails reach the inbox, not spam.
- What Are Pre-Warmed Inboxes? How They Work and Why Cold Emailers Use Them — Pre-warmed inboxes skip the 14 to 21 day warmup period and let you start sending cold emails immediately. Here's how they work, what they cost, and who should use them.
- Cold Email Infrastructure Explained: What It Is, Why It Matters, and How to Set It Up — Cold email infrastructure is the foundation that determines whether your emails reach the inbox. Here's what it includes, why 70% of results depend on it, and how to build it right.
- 5 Best DMARC Monitoring Tools for Cold Email in 2026 — DMARC monitoring tools parse authentication reports. Here are 5 best DMARC tools for cold email teams managing sending domains.
- What Is Email Warmup? Beginner's Guide to Cold Email Inbox Reputation — Email warmup gradually builds sending reputation for new cold email inboxes. Here is what it is, why it matters, and how to do it right (or skip it entirely).