Need to send notification to emails outside the application (eg: abc@gmail.com) and get back the res

Hi Team,

We have a requirement like one of our process using workflow will send a notification to our suppliers personal email id(ex: abc@gmail.com)  regarding the goods required. In that mail body we need to incorporate Accept and Reject buttons to provide the supplier to respond mail whether he Accepts or Rejects the Order. That response of the suppplier should be notified to the User as workflow notification for the particular workflow itemkey.

Please let me now the process for achieving the above requirement.

Thanks in Advance.