We have a hybrid Exchange environment with Office365. I started noticing the "approve/deny" buttons provided by the Outlook FIM plugin no longer worked. The error shown is "This request cannot be approved or rejected because it was received from an unauthenticated sender."
What I figured out was my mailbox is in the cloud but the FIM service's mailbox is on-prem, so technically they are from different Exchange orgs and hence the sender is no longer validated since its like an external sender.
Has this scenario been seen by anyone else or addressed already by MS teams? Is there any way to relax the security on the FIM plugin itself to not do this check as a workaround? I checked through some reg keys and unfortunately didn't find any setting saying "VerifySender=NO"