DKIM vs DMARC: What's the Difference?

DKIM and DMARC are both email authentication protocols, but they serve different purposes. Understanding how they differ—and how they work together—is essential for protecting your domain and improving email deliverability.

The Short Answer

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your emails. It proves the email hasn't been modified and that someone with your private key signed it.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a policy layer. It tells receiving servers what to do when emails fail authentication—and requires that DKIM or SPF results align with your From address.

Think of it this way: DKIM is a signature on a letter. DMARC is the policy that tells the post office what to do if the signature doesn't match.

How DKIM Works

When you send an email with DKIM enabled:

1. Your mail server creates a cryptographic hash of the email content
2. The hash is encrypted with your private key
3. The encrypted hash (signature) is added to the email header
4. Your public key is published in DNS

When the email arrives:

1. The receiving server retrieves your public key from DNS
2. It decrypts the signature to get the original hash
3. It creates its own hash of the email content
4. If the hashes match, DKIM passes

DKIM proves the email is authentic and unmodified. But it doesn't tell receiving servers what to do if verification fails.

How DMARC Works

DMARC builds on top of DKIM and SPF. It does three things:

1. Alignment checking: DMARC requires that the domain in your DKIM signature (or SPF check) matches the domain in your From address. This prevents attackers from using their own valid DKIM signature on spoofed emails.

2. Policy enforcement: You specify what receiving servers should do with emails that fail:

• p=none: Deliver anyway (monitoring mode)
• p=quarantine: Send to spam folder
• p=reject: Don't deliver at all

3. Reporting: Receiving servers send you reports about emails claiming to be from your domain—including failed authentication attempts.

Key Differences

How They Work Together

DKIM and DMARC are designed to complement each other. Here's what happens when an email arrives:

An email passes DMARC if either:

• DKIM passes AND the DKIM domain aligns with the From domain
• SPF passes AND the SPF domain aligns with the From domain

You don't need both to pass—just one with proper alignment.

Can You Have One Without the Other?

DKIM without DMARC: Yes, but you're missing the policy layer. Emails will be signed, but receiving servers won't have instructions on what to do if verification fails. You also won't get reports about authentication failures.

DMARC without DKIM: Technically possible if you have SPF, but not recommended. DKIM survives email forwarding better than SPF. Without DKIM, forwarded emails will likely fail DMARC.

DMARC without both DKIM and SPF: DMARC has nothing to check. All emails will fail DMARC (since neither SPF nor DKIM can pass).

Which to Set Up First

The recommended order:

Check your DMARC configuration at dmarcrecordchecker.com.

What About SPF?

SPF (Sender Policy Framework) is the third piece of the email authentication puzzle. While DKIM verifies the message, SPF verifies the sending server.

| Protocol | Verifies | |----------|----------| | SPF | Is this server authorized to send for this domain? | | DKIM | Is this message unmodified and signed by this domain? | | DMARC | Do SPF/DKIM pass AND align? What's the policy? |

For complete email authentication, you need all three. DMARC uses both SPF and DKIM results to make its decision.

Why You Need Both DKIM and DMARC

Having only DKIM leaves gaps in your email security:

No policy enforcement: Without DMARC, receiving servers decide on their own what to do with failed DKIM. Some might deliver, others might reject. You have no control.

No visibility: DMARC reports show you who's sending email claiming to be from your domain. Without them, you're blind to spoofing attempts.

No alignment requirement: Without DMARC, an attacker could use their own valid DKIM key while spoofing your From address. DMARC's alignment requirement prevents this.

Incomplete authentication: Major email providers like Google and Yahoo now expect DMARC for bulk senders. Without it, you may face deliverability issues.

Monitor Your DKIM Records

Checking once is good. Monitoring continuously is better. The Email Deliverability Suite watches your SPF, DKIM, DMARC, and MX records daily and alerts you when something breaks.