Exchange Hybrid and external email

Copper Contributor


I enabled a ‎Private‎ group to "allow external senders to email this group"

I see it in the GAL. but its failing with a Remote Server returned '550 5.1.1 User Unknown'


What do i need to create on my on-premise exchange to get this to work? My on-premise i think talks to and smtp /spam filter server that probably needs to know about the smtp address.

4 Replies
Define "private group"? Generally speaking, you'd want to toggle the -RequireSenderAuthenticationEnabled flag. But the error message above suggests a different issue.

a new group under Outlook client
that is set to private and appears as a private group under the exchange admin center.

Got that part, but not sure where on-premises Exchange comes into play in your scenario, as Groups are pure cloud objects? In any case, for a Group to start receiving external messages, you'd want to toggle the RequireSenderAuthenticationEnabled flag.
Had to create New-MailContact on premise AD