What is “rewrite-from” and why is it used?
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"Rewrite-from" is the technique mailing list servers use when they need to change the visible From header on a message before redistributing it to subscribers.
The reason they do it comes down to DMARC. When a mailing list relays a message, it's sending from its own infrastructure, not the original sender's. If the original sender's domain has a DMARC policy of p=quarantine or p=reject, and the list can't align its sending with that domain, DMARC will fail. Depending on subscribers' mailbox providers, messages might land in spam or get rejected entirely.
Rewriting the From header to the list's own domain solves the alignment problem. Now the list's DKIM signing and SPF records align with the From address, and DMARC passes for the list's domain. The original sender's DMARC policy is no longer an obstacle.
The downside is that it breaks the direct connection between message and sender. Recipients see the list address in the From field, not the original author. Some list servers handle this by putting the original sender in the Reply-To header, which preserves reply routing at least. But the From display still changes, and in some clients the sender's name disappears entirely.
It's a pragmatic workaround rather than a clean fix. ARC is the protocol designed to handle this more gracefully, by preserving the original authentication state through intermediaries without needing to touch the From header. But ARC adoption isn't universal yet, so many lists still fall back to rewrite-from for compatibility.
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