I don't expect a fundamental shift but the boss having no access to his mails seems certainly like something I would bring up quite a bit.
It will help a bit, but it would need much more than 24h to have a real impact. If their service is still down in a week, now we're talking.
Barring corona & year end holidays, this is probably the closest we can get to a global work holiday.
This means you cannot do anything that requires email auth (OTP, signup etc)
It is much easier to read the code you wrote.
It's such bedrock infrastructure that I've seen it used as fallback in the event of electronic trading infrastructure outage, brokers would accept specifically formatted emails as orders.
At this point it would probably be less impact to have phones go out globally because people would fallback to walking across the floor, using zoom/slack for simultaneous communication or email for more async.
That's why most don't realize how big GMail is. Google has 1.8 billion GMail users, including a great many who are using their Google email professionally (no matter if it's a Google Workspace with their own domain or a redirection or just a plain GMail). Apple has 1 billion email users.
Microsoft 400 million and, granted, many businesses but it's not a fourth the number of email users GMail has.
And many, many, many people (real estate, delivery drivers, Uber and the likes) are using either Apple or GMail email from... Their phones.
It's a good thing it's only the "small" Microsoft email users base that is affected and not the 1.8 billion GMail users.
BBC is running live coverage of it at the level of government and ministers.