Microsoft Adopts ARC For Office 365 Email Mailboxes, Valimail Praises Move

Microsoft is the latest big name to adopt the Authenticated Received Chain (ARC) email protocol, and will feature it within Office 365.

The announcement has drawn praise from industry insiders like Valimail, the co-author of ARC.  

This support will “help expand the trustworthiness and reliability of enterprise email,” states Seth Blank, director of industry initiatives for Valimail. 

In a recent blog post, Microsoft announced that ARC is now enabled for Office 365 hosted mailboxes.

“Before ARC, modifications performed by intermediaries in email routing, like forwarding rules or automatic signatures, could cause email authentication results to fail by the time the email reached the recipient mailbox,” the post says. 

The blog continues, “With ARC, the cryptographic preservation of the authentication results allows Office 365 to verify the authenticity of an email's sender.” 



At first, ARC will be used to verify authentication results within Office 365, but support will be added for third party signers in the future, Microsoft says.  

According to Valimail,ARC helps users to avoid the modifications of message content by mailing lists and secure email gateways. These changes can cause legitimate email to appear as suspicious.

Blank states that “ARC improves the entire email ecosystem, by allowing legitimate mail to flow through mailing lists and SEGs without issue.”

Blank is also chairman of the AuthIndicators Working Group, which has been developing the Brand Indicators for Message Identification (BIMI) standard, a security standard that allows brands with DMARC protection to display their logos in email subject lines.

The AuthIndicators Working Group now includes Valimail, Verizon Media, Google, Validity’s Return Path, Agari, LinkedIn and 250ok. 

Last month, it was announced that CNN had been issued the first Verified Mark Certificate (VMC) for a domain that sends email at scale. It is expected to conduct a BIMI pilot. 

The VMC is a BIMI-related tool requiring that email senders are who they say they are.



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