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What is DKIM Alignment?

DKIM Alignment helps domain owners verify the sending domain's authority over the sent email. This is done through 2 signatures found in the message body (appended during DKIM signing). The domain names displayed in both the signatures give away the true identity of the sender: 

1. The mail From: domain

2. The domain in the d= tag in the DKIM-Signature header (DKIM signing domain) 

DKIM alignment modes (included in your DMARC record)

1. Relaxed (adkim=r) :  an organizational match between the  the DKIM signature domain and the mail From: domain is enough for DKIM alignment to pass, instead of an exact match. 

2. Strict (adkim=s) : an exact match between the  the DKIM signature domain and the mail From: domain is is needed for DKIM alignment to pass. 

Example 1: DKIM alignment passed

DKIM-Signature: v=1; ...; d=domain.com; ...

From: [email protected]

The domain name (domain.com) in the DKIM signature header perfectly matches the domain name in the mail From: header. Hence DKIM alignment passes.

Example 2: DKIM alignment failed

DKIM-Signature: v=1; ...; d=xyz.org; ...

From: [email protected]

The domain name (domain.com) in the DKIM signature header does not match the domain name in the mail From: header. Hence DKIM alignment fails.

DKIM pass exception: Using a relaxed DKIM mode of enforcement

Example: 

DKIM-Signature: v=1; adkim=r...; d=domain.com; ...

From: [email protected]

The domain name (domain.com) in the DKIM signature header matches the organizational domain name in the mail From: header. Since the DKIM alignment mode is set to relaxed (adkim=r),an organizational match is enough for DKIM alignment to pass, instead of an exact match. 

Note: DKIM alignment mode if set to adkim=s (strict) will lead to alignmnent failures in case of organizational domain matches 

DKIM Alignment >What is DKIM Alignment?
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Advanced Email Authentication Course