A random story that just popped back into my head while reading another rant:

Long ago, we developed our own webmail platform at the request of clients. After it was finished, it was never updated and eventually turned into an outdated insecure steaming pile of crap. Up until ~2015, it looked like the first iteration of AOL Mail from the 1990s (and it functioned as such too.) Years, we decided to sunset the platform, and allotted 6-months or so to transition all the active users off the platform and over to an alternative email provider. We had to call each client multiple times and send multiple emails with a deadline detailing when the service would be shut down, and we'd explain that if they didn't transition over to a new service and transfer all their emails before that date, then the emails would be lost forever. Lo and behold, a handful of clients ignored our repeated contact attempts, and we shut down their email service (as we told them that we would.) Of course, they called screaming and panicking "OUR EMAIL IS DOWN OUR EMAIL IS DOWN WE'RE LOSING MONEY FIX IT NOW!!!!," and we told them "We attempted to contact you multiple times, and you neglected to return our numerous calls or emails. We're happy to help you transition your old email addresses to this new provider, but because you neglected to follow the cushy deadline we provided you, all of your emails are gone."

Of course, they denied having ever received our calls/emails, and we'd have to provide them with our outgoing call recordings to prove that we did in fact contact them multiple times. Then they'd blame the mishap on their secretary, who would blame it on the intern, who would blame it on the IT guy, who would blame it on the janitor, and so on and so forth.

Moral of the story: always keep outgoing call recordings when you're sunsetting a product.