Forwarding and mailing lists are the largest source of legitimate DMARC failures. ARC lets receivers accept mail that would otherwise be quarantined under p=reject.
How to implement ARC (Authenticated Received Chain)#
- Check whether your inbound gateway or mailing-list software supports ARC sealing.
- Enable ARC sealing on any system that modifies and re-sends mail.
- Verify ARC-Seal, ARC-Message-Signature, and ARC-Authentication-Results headers appear on forwarded mail.
- Confirm downstream receivers (Gmail, Microsoft) honor your seals by checking Authentication-Results for arc=pass.
How to verify it worked#
Send a test message to seed mailboxes at Gmail, Outlook, and Yahoo, then inspect the Authentication-Results and delivery headers. Repeat after any DNS or sending-platform change.
Common mistakes#
- Expecting ARC to fix your own outbound authentication; it only helps intermediaries.
- Trusting ARC from unknown sealers, which reopens the spoofing door.
Frequently asked questions#
Do I need ARC as a sender?
No. ARC is implemented by intermediaries and receivers. Senders benefit indirectly when their mail is forwarded.
Which providers honor ARC?
Gmail, Microsoft, and Yahoo all evaluate ARC when deciding whether to override a DMARC failure.