Why do ESP forwarders benefit from ARC?
Still have a question, spotted an error, or have a better explanation or a source we should cite?
If you're running a mailing list or forwarding service, ARC is a real fix. Here's why.
When you forward an email, you're changing the envelope sender to your own domain. That's actually necessary for delivering to your subscribers. But it breaks both SPF and DKIM alignment. The original sender's domain and your forwarding domain don't match anymore. So if someone has set p=reject on their DMARC policy, the receiving mail server sees an alignment failure and bounces the message.
Before ARC existed, this was a huge problem. People couldn't run mailing lists safely with strict DMARC policies. Subscribers wouldn't get the forwarded mail.
ARC solves this. As the forwarder, you add your own ARC seal to the message. You're signing a record of the original authentication: "SPF passed for domain.com, DKIM passed for domain.com." When the message arrives at the final destination, the receiving server trusts your ARC seal (because you're a known, legitimate forwarder). It can then honor the original authentication results instead of rejecting the message based on alignment failure.
This only works if you're using a reputable forwarder that receivers trust. Google Groups, major ESPs like Mailchimp, and established mailing list platforms already do this. But if you're running your own forwarding service, you need to implement ARC properly and build trust with receivers.
Next step: if you're setting up forwarding, learn how to properly implement ARC signing, and understand how SPF, DKIM, and DMARC interact.
Contributors
Who worked on this answer
Every name links to their profile. Every company links to their site. Real people, real accountability.
