incoming emails should be automatic forwarded to external, but disable the right to send emails via outlook to external

Hello, 

Customer requested this Procedure:

Exchange User Emailbox has a permanet forwarding to one external "Email-Contact" (in ms exchange 2010 settings)

But, please disable the right to send external Emails from the Outlook / OWA / EAS iPhone  .

Is that possible?

Thx in advance!