Why does forwarding break SPF alignment?
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SPF failing and SPF alignment failing are two different problems. You can have SPF pass (the forwarder's IP is on their own list) and still fail alignment (the domain doesn't match the From header). With forwarding, you usually get both failures at once.
Here's the alignment part specifically. SPF alignment checks whether the domain in the Return-Path header matches the domain in the From header. When you send email, your Return-Path (the envelope sender) typically matches your From domain. Alignment passes.
When a forwarder re-sends your email, it changes the Return-Path to its own domain. That's normal behavior. The forwarder is now the delivery agent responsible for that message. But your From address is still your original domain. Now the Return-Path domain and the From domain are different. SPF alignment fails.
This matters because DMARC needs at least one aligned pass to let the email through under a strict policy. If DKIM also fails (because the forwarder modified the message), DMARC fails entirely. With a p=reject policy, that means the email gets dropped.
You can check your DMARC policy and alignment settings with our free DMARC parser. If forwarding is causing regular alignment failures, they'll show up in your aggregate reports.
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