Notify! Back in Stock|PreOrder

UPDATE: The developer responded to my review, apologized, and added new features to the app to prevent emails from being sent automatically when the # of people on the waitlist exceeds the inventory quantity, which is what caused the issue in our case. I'm updating my review due to their responsiveness in correcting the issue. This app just just emailed 2,000 people and told them our products were back in stock when they were not, and then the app just crashed (504 error when I try to access it) so I can't even get into the app so I can email those customers and apologize.