While sending emails to users from a sharedmailbox using firstname.lastname@example.org email to various users inside the organization, results into bounce back into sharedmailbox similar to :
( Sharedmailbox is on Office365 )
From: System Administrator
Your message did not reach some or all of the intended recipients.
Subject: This is Subject Line
Sent: 4/16/2018 9:05 AM
The following recipient(s) cannot be reached:
UserA on 4/16/2018 9:05 AM
This message could not be sent. Try sending the message again later, or contact your network administrator. You do not have the permission to send the message on behalf of the specified user. Error is [0x80070005-0x0004dc-0x000524].
I tried running following command to take a look if this userA have send on behalf rights to this mailbox and looks like he already does:
Get-Mailbox -Identity SharedMailbox | FL GrantSendOnBehalfTo
UserA, UserB, User C ...
Many bounce backs are going into Sharedmailbox directly.
Can anyone point me to where this issue could be ?