Let’s suppose you have a website with an e-commerce plugin.  A user comes in, buys a product and goes fine through the checkout process, but when the site tries to redirect the user to the third-party gateway where he wants to pay, something goes wrong. The redirect goes to a 404 page or never gets done. And that only happens with that single costumer. All the other costumers who bought that same product from your site did it without an itch. Whatever the problem is, you need to debug locally to find the source of it.

So now you need to replicate the process in your local mirror of the production site. You click the “buy now” button in the product page, then go to the checkout page and fill the form with the very same values that the user has previously entered. You click “confirm purchase”, and then notice the error through your favourite Javascript profiler: the email of the user customer has a character that your validator doesn’t like, so you need to improve it, but somehow the form was sent either way instead of prompting the user to re-enter his email, and you need to fix that too.

A couple of minutes later, while you’re fixing your code, you receive a phone call from the customer, who says that he received a second purchase confirmation email for an operation he did not perform. Then you have to explain to him that you were working on the issue that he reported earlier, and he understands but insists on the fact that he was bothered for a second time (the first one being his impossibility to pay) and that you should be a little bit more professional. And he is right. Now let’s suppose that this email thing happens often, and that you even lost sales because of this. The same can be applied to other scenarios regarding emails being sent, such as creation of testing users, or posting test contents to a blog with a lot of suscribers that should be notified of new posts by email. I’m sure you don’t want this. I really don’t for sure.