Configuring Send on Behalf permission for a shared mailbox in Exchange Online

Most of you guys must have noticed that you do not have the option to configure Send on Behalf permission for shared mailboxes in O365. This can be done only using the PowerShell. The below command could be run on PowerShell to achieve this:

Set-Mailbox -Identity test@contoso.com -GrantSendOnBehalfTo testuser

where, ‘test@contoso.com’ is the shared mailbox and ‘testuser’ is the user account or mailbox for which the permission is assigned.

You can confirm the above operation by using the below Get-command

Get-Mailbox -Identity mailbox | FL GrantSendOnBehalfTo

Reference : https://technet.microsoft.com/en-us/library/jj919240(v=exchg.150).aspx