HubSpot does not support ARC signature, and we’d love it if it did.
Authenticated Received Chain (ARC) is a protocol that preserves your email’s authentication results (SPF, DKIM, DMARC) across forwarding and intermediary steps.
Why does this matter? Well, not all mail passes directly from sender to recipient. Which means that SPF, DKIM, and DMARC alignment failures can occur, and your messages aren’t delivered.
Meaning that even though the original sender (you) is legitimate, they can fail DMARC.
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ARC needs to be defined on the email headers by HubSpot and should not need any configuration by users (other than maybe the option to enable/disable).
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You can read more about ARC here: ARC - Authenticated Received Chain | DmarcDkim.com