Envelope and header From

DMARC aspf and adkim choose strict or relaxed alignment. Relaxed compares organizational domains. Strict requires an exact host match.

Providers that send on behalf of customers often need DKIM alignment because the envelope remains at the provider while the header From shows the customer domain.

The reverse-path from MAIL FROM receives non-delivery reports. That address may differ from the From header the recipient sees, which is why DMARC alignment is defined separately from mailbox display.

Postmark's provider page on this site documents Return-Path at a subdomain and relaxed SPF alignment (aspf=r) when the envelope uses that subdomain.

RFC 5321 defines the reverse-path in MAIL FROM. Receivers that enforce DMARC still evaluate SPF against that address, not against the display name in the From header.

Relaxed alignment compares organizational domains. A MAIL FROM at bounce.vendor.com can align with From at news.example.com when adkim and aspf are relaxed and the organizational domain matches.

Strict alignment requires exact host matches. SaaS products that keep the envelope at the vendor domain often rely on DKIM with d= set to the customer domain instead of SPF alignment.

The Return-Path header, when present, often mirrors the envelope address used for bounces. DMARC SPF alignment still keys off the domain used in the SPF check, not the header alone.