Mail triggering!!!!

Hi,

I need a same mail to be triggered each time when I get the status "To be Approved".

Eg :- Initial status is " To be Approved" - Mail should go to the Change Manager (CM)

Action " Rejected" is performed by CM and status changes to " rejected" .

Then again " to be approved " action is performed and the status changes to "To be Approved" and

when this status is reached again the same mail should go to the CM.

How to do this?