Microsoft recently announced in an update that it is working to add custom Authenticated Received Chain (ARC) configuration support to Microsoft Defender for Office 365.

Activating ARC for Office 365 hosted mailboxes prevents email authentication from falling due to modifications made during routing thereby preserving results at every level.

While Microsoft stated that the new feature will be widely available on web platforms from March 2022, the ability to customize ARC configurations to include additional trusted intermediaries, modify messages with attributions while also linking their signatures with their domain names thereby keeping the ARC chain intact.

According to Microsoft, “Email senders use authentication mechanisms like SPF, DKIM, DMARC to authenticate emails, but some legitimate intermediate services may potentially make changes to the email, which might cause the email to fail authentication at subsequent hop. With this change, admins will be able to add trusted intermediaries in the Microsoft 365 Defender portal to allow Microsoft to honor these ARC signatures, thereby allowing legitimate messages.”