Could you please help me figure out a way using which i need to send a mail to OUTLOOk having 2 buttons "approve" and "reject" and how i can recieve the value back for whatever options are chosen.
<quibbling over words>You can't send anything to Outlook - it's a client application. You can only send something to a mail server like Exchange.</quibbling over words>
The easiest would probably be to send a link to a web app that shows a page containing those two buttons, and which can evaluate a form submission and do whatever you want done with the results. if you want to disambiguate between users, you can append an encrypted userID as a parameter to the link.