GrantSendOnBehalfTo

Question

Hi All

i am using exchange 2016 hybrid environment, i have created remote shared mailbox in onprem. i have provided GrantSendOnBehalfTo Permission to one of the user to this shared mailbox using the below syntax but user is getting the below error. its working from web mail. please guide me

Set-Mailbox -Identity "sharedmailbox@Company portal .com" -GrantSendOnBehalfTo "user1@Company portal .com"

Your message did not reach some or all of the intended recipients.

  Subject:	test  
  Sent:	6/20/2021 11:00 AM  

The following recipient(s) cannot be reached:

  User2 on 6/20/2021 11:00 AM  
        This message could not be sent. You do not have the permission to send the message on behalf of the specified user.   

Answer 1

@Roger Roger

There doesn't exist send on behalf permission for shared mailbox, although it can be added using the command, it is still not supported. Here are only exist full access and send as permission for Shared mailbox:

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Answer 2

Where does it say its not supported?

This document says it is:
https://learn.microsoft.com/en-us/exchange/recipients/mailbox-permissions?view=exchserver-2019

If its not working, verify the mailbox isnt hidden.