Folks, As email passes thru our network, we make changes to the message. We may add items to the header/footer or change links into "protected mode". Doing so breaks Authentication.
Authenticated Received Chain (ARC). ARC helps preserve authentication results across intermediaries. Learn more about ARC and how we make it work here: Improving "Defense in Depth" with Trusted ARC Sealers for Microsoft Defender for Office 365 - Microsoft Tech Community<https://techcommunity.microsoft.com/t5/microsoft-defender-for-office/improving-defense-in-depth-with-trusted-arc-sealers-for/ba-p/3440707> We have used ARC for a while, but this is the first time we rolled it out to our 0365 customers. That said... there are some email filtering vendors that are not using ARC which breaks authentication. In those cases, we are forced to bulk or reject legitimate email sometimes from our own customers who use email filtering services. Thanks, Jeff Dellapina Sr. Email Delivery Manager SAGE Team [X]
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