[Solved] Remove Send on Behalf to a Active Directory user

Hello,

I am trying to remove the send on behalf permission to a Active Directory user from a mailbox. The command

Set-Mailbox "destinationMailBox" -GrantSendOnBehalfTo @{remove="ADUser"}

doesn't work, because is expecting a mailbox at the remove object. The presented error is:

Couldn't find object "ADUser". Please make sure that it was spelled correctly or specify a different object.
    + CategoryInfo          : NotSpecified: (:) [Set-Mailbox], ManagementObjectNotFoundException
    + FullyQualifiedErrorId : [Server=MAILSERVER,RequestId=46c6baa6-cd57-41bc-b1d8-dbaac4905299,TimeStamp=19/07/2016 09
   :55:11] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] 9232C277,Microsoft.Exchange.Management.Recipien
  tTasks.SetMailbox
    + PSComputerName        : MAILSERVER.domain.local

We use Active Directory user (ADUser) that doesnt have a native email address (p.e. aduser@domain.com).

I try to find without answer the solution for this question on the internet.If already exits a thread on this forum for this question, please redirect me for the correct one.

Thank you,

Mark