Mean Time to Recovery (MTTR) explained
It's Friday afternoon, and you have mail. Apparently, a user received a 500 error when attempting to sign in. She contacted Customer Service. They didn't know what to do, so they forwarded the email to your engineering team. A close look at the email thread reveals that Customer Service received it... on Tuesday. And they sat on it until today. Hopefully, it was just this one user. You open your browser, navigate to the web application, and attempt to sign in. You also get a 500 error.