DMARC adkim= Tag — DKIM Alignment (adkim)

The DMARC adkim tag controls how strictly the DKIM d= signing domain must match the From header domain. "r" allows subdomain matches; "s" requires exact match.

Importance
Optional
Tag
adkim=
Default
r (relaxed)
Example
adkim=r

✅ Valid Values

r Relaxed (default). Organisational domain matching — subdomains align with parent.
s Strict. The DKIM d= value must exactly match the From header domain.

💬 What This Tag Does

The "adkim" tag controls how strictly DMARC compares the DKIM signature's "d=" domain with the email's From header domain. Relaxed mode ("r") allows the DKIM domain to be a parent domain (e.g., DKIM signed by "example.com" aligns with From "mail.example.com"). Strict mode ("s") requires an exact match.

📚 RFC References

↗RFC 7489 §3.1 — Identifier Alignment

🔗 Related DMARC Tags

aspf=
SPF Alignment (aspf)

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