Status of ARC
The Authenticated Received Chain, or ARC, was adopted as an official work item of the IETF DMARC Working Group in June 2016, and the specification was published as RFC 8617 on July 9th, 2019.
Google has deployed ARC in their email services, code libraries and a test suite are freely available, several commercial MTAs and email services already include ARC support, and patches for popular mailing list managers (MLMs) have been released. Links to these items are available on our Resources page.
What is ARC?
When an email sender or Internet domain owner uses email authentication to make it easier to detect fraudsters sending messages that impersonate their domain, some services like mailing lists or account forwarding may cause legitimate messages to not pass those mechanisms, and such messages might not be delivered. These services may be referred to as intermediaries because they receive a message, potentially make some changes to it, and then send it on to one or more other destinations. This kind of email traffic may be referred to as an indirect mailflow.
ARC preserves email authentication results across subsequent intermediaries (“hops”) that may modify the message, and thus would cause email authentication measures to fail to verify when that message reaches its final destination. But if an ARC chain were present and validated, a receiver who would otherwise discard the messages might choose to evaluate the ARC results and make an exception, allowing legitimate messages from these indirect mailflows to be delivered.
How can I learn more?
- You can read RFC 8617, the specification for ARC.
- You can read the current draft of the recommended usage document for ARC.
- General questions about ARC should be brought to the arc-discuss list operated by DMARC.org. Feel free to visit the list information and subscription page. Please note that this is a technical forum intended for IT professionals, programmers, network operators, etc. Consumers or end-users should contact their service provider’s help desk for assistance.
- Further review and development of the protocol would be carried out in the IETF DMARC Working Group. Instructions for subscribing are available on the list information and subscription page. If you join, please take the time to read through the list archives and familiarize yourself with the discussion to date.
- You can also read the original press release that announced the ARC protocol in October 2015
What are the next steps for ARC?
Now that ARC has been published as RFC 8617, implementation of the protocol will speed up. If you are a mailbox provider or intermediary (mailing list operator, message forwarder), you should be implementing ARC.
Google has added ARC verification and sealing to their email services (Gmail, G Suite, and Google Groups). The popular Mailing List Manager (MLM) software Sympa incorporated ARC in v6.2.38, and ARC is being incorporated into the next release of the Mailman MLM – in fact ARC configuration directives are already in the online documentation.
The commercial MTAs Halon and MailerQ incorporate ARC, and the milters authentication_milter and OpenARC can be used to deploy ARC with the Postfix, Oracle Communications Messaging Server, and Sendmail MTAs. Several open source libraries and modules are already available for those who need to integrate ARC functions into their systems.
Be sure to check our Resources page for a more complete listing.