It affects a lot more than just Microsoft and their services. Imagine all the 2 factor logins where the code is send by mail, such as payment processors or other services with high security. They'll still work but the users can get locked out. If this continues for a little longer, we'll start to see some real consequences worse than just email being down.

Other mail providers are working, so we could just send mails through those, but with Microsoft having the majority of business market share, you probably shouldn't expect to receive a reply from anyone using it. Just another way it is disrupting a whole lot of people who have jack shit to do with Microsoft.