How to define workflow for PO release so that mail can be sent to the sap inbox

Dear All,

As per the business requirement we have defined "n" level release strategy.

Now, we want to define work flow as follows:

When PO is created then mail should goes to the sap inbox of user 1.

If user 1 is approved the PO then again mail should goes to user 2...so on.

Kindly help on the same.

Thanks in advance!!

Thanks & regards,

Archana Londhe