Use this parameter to grant the trusted user Send On Behalf Of permissions to the mailbox specified by the Identity parameter. ...

Use this parameter to grant the trusted user Send On Behalf Of  permissions to the mailbox specified by the Identity parameter. This parameter accepts the arguments True or False. These arguments are not case sensitive. When using a CSV file, specify GrantSendOnBehalfOf True to grant the permission or GrantSendOnBehalfOf False to not grant the permission. Specifying False will not remove the permission if it is already set. To remove the permission, use Remove-MSOnlineMailPermission.