Hi Rohit
"Now what i want is instead of going in sap inbox the user should be able to take decision through the link send on his mail id."
Do you want the link to open UWL and then user can Approve / Reject? If yes, then Rob and & Ronen have given the right way.
or
Do you want the capability of Approving/Rejecting directly from email?
If yes, then there is a lot of development required for offline approvals.....here are the links to achieve that:
Offline/External Mail Approval Process without using SAP Part-1 :
http://scn.sap.com/docs/DOC-50456
Offline/External Mail Approval Process without using SAP Part-2:
http://scn.sap.com/docs/DOC-50457
Offline/External Mail Approval Process without using SAP Part-3:
http://scn.sap.com/docs/DOC-50458
Offline/External Mail Approval Process without using SAP Part-4:
http://scn.sap.com/docs/DOC-50532
Regards,
Modak