SPF Alignment
The DMARC requirement that the SPF-authenticated MAIL FROM domain match the visible From: header domain.
SPF alignment is the bridge between SPF (which validates the SMTP MAIL FROM, also called the Return-Path) and DMARC (which judges authenticity based on the visible From: header). A message passes DMARC via SPF only if SPF passes AND the MAIL FROM domain aligns with the From: domain. Strict alignment (`aspf=s`) requires an exact match; the default relaxed alignment (`aspf=r`) accepts an organisational match (e.g., bounces.example.com aligns with example.com). Many third-party senders break alignment by using their own bounce domain, which is why DKIM (with its own alignment rule) is usually the more reliable DMARC pass path.