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.
Published · Last verified · Maintained by TamingDNS
Optional
adkim=
r (relaxed)
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.
📋 Complete Example Records
Every one of these is a complete record you can paste as it stands. Each goes in a TXT record at
_dmarc.yourdomain.com. Check yours with the
DMARC Checker
or assemble one in the
DMARC Builder.
v=DMARC1; p=reject; rua=mailto:dmarc-feedback@example.com
No "adkim" tag, so relaxed applies. A signature with d=example.com aligns with a From address at news.example.com, because both share the organisational domain.
v=DMARC1; p=reject; adkim=s; rua=mailto:dmarc-feedback@example.com
Strict changes that. The signing domain now has to be identical to the From domain, so the same d=example.com signature no longer aligns with news.example.com.
v=DMARC1; p=reject; adkim=s; aspf=s; rua=mailto:dmarc-feedback@example.com
Both identifiers strict. Check your bulk senders first, since a provider that signs with its own subdomain will stop aligning the day you publish this.
v=DMARC1; p=reject; adkim=s; aspf=r; rua=mailto:dmarc-feedback@example.com
Mixed modes are legitimate. DKIM is pinned exactly while SPF stays relaxed, which suits setups where the bounce address sits on a subdomain.
📚 RFC References
🔗 Related DMARC Tags
🛡️ Related Tools
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