Secure architecture design – How Defender for Office 365 protects against EchoSpoofing

Hi RaffaColavecchi-MVP 

It seems to me that the redirecting issue also exists when the recipient address is a mailbox.

RossAdams although it is not a relaying issue but a redirecting issue, the effect is similar to echo spoofing as if an internal address is spoofed in the Header From, then the redirect process authentify the message by applying an aligned DKIM signature.

DMARC fail on the incoming message, but DMARC pass when it leaves the tenant after having been redirected.