Why is ARC needed for email forwarding?
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Here's the problem. Your employee forwards a work email to their personal Gmail account. The forwarder's IP isn't in the original sender's SPF record. So SPF fails. If the forwarder adds a footer or modifies the message at all, it breaks the DKIM signature too. Now both SPF and DKIM are broken. That means DMARC alignment fails, and with a strict policy, the forwarded email gets blocked.
That's where ARC comes in. ARC (Authenticated Received Chain) lets the forwarder add cryptographic proof that the message was authentic before it passed through. It creates a signed chain showing "I verified this email at my hop, even though forwarding broke the original signatures." Gmail and Outlook trust that chain and let the message through.
Without ARC, legitimate forwarded emails just vanish into spam folders. With it, they arrive. That's the whole reason ARC exists. Now's the time to learn how ARC actually works so you can spot when your forwarding setup needs it.
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