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On-Prem Mailbox Unable to Send to 365 Group


I am currently running in a hybrid environment where mail is being routed on-prem. I have a group that when I try to send a message to from an on-prem mailbox it fails with the following error:

RecipientStatus : {[{LED=550 5.7.133 RESOLVER.RST.SenderNotAuthenticatedForGroup; authentication required; Delivery restriction check failed because the sender was not authenticated when sending to this group};{MSG=};{FQDN=};{IP=};{LRT=}]} 

I have already confirmed the following:

  • RequireSenderAuthenticationEnabled is set to False for the 365 group
  • Per these instructions I have set the msExchRequireAuthToSendTo in the rule to False, however once the sync occurs it’s set back to TRUE.

I have a feeling this started after I upgraded Azure AD Connect to the newest version a few months ago, but it was just reported recently.

Anyone have any other suggestions what to check or workaround for this?

submitted by /u/cpres2020
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