Mail Notification based on workflow steps

Dears,

we have integration between SAP and Extended XECM For SAP,

we have a requirements that while PO is created in SAP and being on Approval Cycle (workflow), for each change in the transaction in every workflow step i want to send notification from OPenText to the creator.

the problem i faced that how can i track the change during the approval cycle and detect the user who make the change?

is sending notification more applicable from SAP or OPenText?