Granting 'Send As' Permission in Exchange 2007

Granting 'Send As' Permission in Exchange 2007

Hi, the granting of this permission seems to be missing. I am running the latest version. I can grant 'full mailbox access' and 'send on behalf' but cannot grant the 'send as' permission. Can you advise if this is in the works?
 
Regards,
 
GAC