Send on behalf and read receipt

Hi all.

I am migrating a customer infrastructure from Exchange 2007 to Exchange 2013. The problem is about read receipts with send on behalf mail, that work differently in Exchange 2007 and Exchange 2013.

Let's suppose that user X sends on behalf of user Y.

In Exchange 2007 the read receipts arrive in user Y mailbox. In Exchange 2013 the read receipts arrive in user X mailbox (and this is a big problem for the customer).

I'm trying to change the Disposition-Notification-To header with a transport rule, but I always receive an error (You cant set header Disposition-Notification-To with value). I cannot create an Outlook rule without adding something specific in the message object or body (and it is not possible for the customer). I have not Transport Edge role in my infrastructure

Has anyone found a solution for this kinf of problems?

Thanks!
Lu