As part of the case design, after someone completes a purchase, the application should send...

To ensure that a confirmation email is sent after a purchase is completed within a case, incorporating this functionality directly into the case life cycle is crucial. The most straightforward and effective way to achieve this is by designing it as a distinct step in the process.

D. As a separate process step: Adding the action of sending a confirmation email as a separate process step immediately following the completion of a purchase allows for clear, logical sequencing in the case design. This approach ensures that the email is sent as an integral part of the case progression, directly linked to the purchase completion event.

Configuring it as part of the stage configuration (A) or as an alternate stage (B) might not provide the direct, immediate linkage to the purchase completion action that is necessary for timely email dispatch. Considering it as part of the general case configuration (C) is too broad and does not specify where in the case life cycle the email should be sent.