Identifier Alignment (DMARC)

What is Identifier Alignment in DMARC?

Identifier alignment is a core concept in DMARC that ensures the domains used in authentication checks match the visible domain shown to recipients. In simple terms, it verifies that the technical senders (used by SPF and DKIM) align with the human-readable “From” address that appears in the email header. Alignment protects users from spoofing attacks that exploit domain mismatches to appear legitimate.

Without identifier alignment, attackers could pass SPF or DKIM using unrelated domains, making fraudulent messages look authentic. DMARC enforces alignment to ensure that both the visible and authenticated domains belong to the same organization or subdomain structure.

How Identifier Alignment Works

When a receiving mail server evaluates DMARC, it performs two key checks:

• SPF Alignment: Compares the domain in the Envelope From address with the domain in the visible From header.
• DKIM Alignment: Compares the domain in the DKIM “d=” tag (the signing domain) with the visible From header.

If either SPF or DKIM passes and aligns with the From domain, the message passes DMARC authentication. If neither mechanism aligns, the message fails DMARC and is processed according to the domain’s published policy (none, quarantine, or reject).

Example:

In this example, both SPF and DKIM domains align with example.com, resulting in a DMARC pass.

Strict vs. Relaxed Alignment

DMARC supports two alignment modes for both SPF and DKIM, controlled by the adkim and aspf tags in the DMARC record:

• Relaxed alignment (default): Allows subdomains to align with the organizational domain (e.g., mail.example.com aligns with example.com).
• Strict alignment: Requires an exact domain match (e.g., billing.example.com does not align with example.com).

Example DMARC record with strict alignment:

Strict alignment increases protection against spoofing but can cause false rejections if subdomains or third-party senders are not configured properly.

Why Identifier Alignment Is Important to Email Authentication

Identifier alignment is what makes DMARC stronger than SPF or DKIM alone. It ensures that authentication isn’t just technically valid, but also contextually correct. Without alignment, an attacker could send messages from an unrelated domain that still pass authentication, misleading recipients.

Alignment helps prevent:

• Domain spoofing
• Phishing attacks impersonating trusted brands
• Fraudulent messages sent via unapproved third-party platforms

Proper alignment also improves email deliverability by signaling to mailbox providers that the sender’s domain is authenticated and legitimate.

Identifier Alignment and DMARCeye

DMARCeye continuously analyzes SPF and DKIM alignment across all domains and subdomains. The platform visualizes where alignment fails, identifies unauthorized senders, and helps fine-tune DMARC policies to ensure proper enforcement.

By correlating authentication results with alignment data, DMARCeye highlights which senders pass SPF or DKIM but fail alignment—indicating potential misconfigurations or spoofing. This insight allows security teams to optimize domain security and confidently move toward a full DMARC enforcement policy.

Sign up for a free trial of DMARCeye today and secure your email domain.

To learn more about DMARC and DMARC-related terms, explore the DMARCeye Glossary.