Email Authentication
The umbrella term for protocols (SPF, DKIM, DMARC) that verify a sender's identity and prevent email spoofing.
Email authentication is the collective set of protocols that prove an email genuinely originated from the domain it claims to be from. The three core protocols are SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance). Together, they form a layered defense against spoofing, phishing, and domain impersonation.
How the three protocols work together:
- SPF verifies that the sending server's IP is authorized by the domain owner
- DKIM cryptographically signs each email, proving it hasn't been altered in transit
- DMARC ties SPF and DKIM together with a policy that tells receiving servers what to do when checks fail, and provides aggregate reporting
Why authentication is non-negotiable: Since February 2024, Google and Yahoo require all bulk senders (5,000+ messages/day) to have SPF, DKIM, and DMARC properly configured. Emails from unauthenticated domains are increasingly rejected or sent to spam. SendSure's Deliverability Testing tool checks all three protocols and grades your domain's authentication setup from A to F.
Related terms
SPF (Sender Policy Framework)
A DNS record that specifies which mail servers are authorized to send email on behalf of your domain.
DKIM (DomainKeys Identified Mail)
A cryptographic email authentication method that verifies an email was sent by an authorized server and wasn't altered in transit.
DMARC (Domain-based Message Authentication)
A protocol that tells receiving servers what to do when SPF or DKIM checks fail for your domain.
BIMI (Brand Indicators for Message Identification)
An email standard that allows brands to display their verified logo next to emails in the recipient's inbox.
Sender Reputation
A score assigned by ISPs to your email sending domain/IP that determines whether your emails reach the inbox.
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Blog posts on verification and deliverability.