So, a product owner created a ticket with the text from headline of the article. You got it into sprint and started to work on it. How will you implement it? Usually we think that e-mail notification is something asynchronous. We can send it anytime. Commonly at night, when our server is under low load. User will read it in some time, but not right after you have sent it. It was true before we have gotten smartphones. Nowadays most of e-mails come instantly with loud notification sound. And user will not pleasured to hear this at sleep time. Therefore I think it is not a good idea to send e-mails at night. So next time you will implement such feature think about it.
P.S. Thanks to LinkedIn for this article. I am very happy to get notifications at 3AM when someone from my connections is celebrating a work anniversary. That is completely what I need to have a good night. And guys... I pointed my location in the profile. It would help to detect my time zone.