aspf

aspf is a DMARC policy tag that specifies how strictly SPF (Sender Policy Framework) alignment should be checked when evaluating email messages. It is part of the Domain-based Message Authentication, Reporting, and Conformance (DMARC) standard and is included in a domain’s DMARC DNS TXT record.

The aspf tag controls SPF alignment mode, with two possible values: r for relaxed and s for strict. In relaxed mode, the domain used for SPF alignment may be a subdomain of the From header domain. In strict mode, the domains must match exactly. The alignment check compares the domain in the SPF authentication result (the envelope from domain) with the domain in the message’s From header, according to the chosen mode.

If aspf is not specified in a DMARC record, the default behavior is relaxed alignment for SPF. This means that messages passing SPF authentication are considered aligned as long as the envelope domain is a subdomain of the From domain, or matches more closely under relaxed rules. The aspf setting works together with the adkim setting for DKIM alignment and with the overall DMARC policy to determine whether a message passes DMARC alerts or is quarantined or rejected.

In practice, domain operators use aspf to balance strictness and deliverability. For example, a domain that sends legitimate mail from multiple subdomains might choose relaxed SPF alignment, while a domain that requires tighter control might choose strict alignment. References to aspf appear in DMARC policy implementations and RFC 7489.