Why has my Outlook mail suddenly stopped connecting to my MacBook Pro mail app?

It appears that in the short-term this is a Microsoft issue. Microsoft announced on 2/2 that EWS was going away in October of this year, but it seems they may have done something to disable it early for some. Apple's Mail app still uses EWS to connect to M365 while the iOS/iPadOS and Outlook do not. We submitted a ticket yesterday to Microsoft after noticing no EWS connections to our Microsoft 365 tenant took place after Sunday, 2/1. As of this morning (2/5) it is now working again for our customers. In the long-term, since EWS is being retired in October, Apple's Mail app for macOS will need to be updated to use the Graph APIs vs. EWS in order to continue functioning.

Same problem here and it seems to be affecting our entire organization, which moved to Microsoft mail a few months ago. The problem started yesterday (February 3) intermittently, but it's now fully broken. It affects Apple Mail on macOS, but not Apple Mail on iOS. Web mail is unaffected, so our users are using outlook.office.com/mail through a web browser as a temporary workaround. The auto-generated AI fixes are useless.

Using Safari or Chrome...search "OUTLOOK LOGIN"....respond to required fields...ie EMAIL ID etc....

Our tech dept. is in touch with both Apple and Microsoft and hopes to have an idea of what's going on by tomorrow. I'll post back if I get any further info.

I'm honestly a little mystified over how it's affecting some users (us, you) but does not appear to be chronic/widespread.

Mine stopped connecting around 12:00pm today...2/4. EXCHANGE Offline....tried EVERYTHING....APPLE Support even had me reinstall TAHOE. Btw, this is a new MacBook Pro, about 2 months old. As others stated, been using OUTLOOK mail server for many years(HOTM]AIL), use Apple mail as mail handleer on the mac and Iphone. iPhone unaffected, Mail App fine. Fortunately we're able to use Web access to Outlook Mail on the Mac time being. Aggravation point: On phone for hours with tech supoport....when I raised possibility APPLE/OUTLOOK Comm handshake issue....response "we haven't heard this problem from others...followup with MicroSoft. I'm beginning to wonder if MicroSoft 365Basic no longer compatible? Must move fro $19.98/Yr to $99 / Yr. If thats solutioin fine....waiting this out bit more, see what happens????

Mine stopped working today. Never had a problem prior to this. Access on ios is fine. But through the Mail app on my Mac, it stopped connecting to my Outlook.com account. I tried removing the account and adding it back, but it won't download any messages after doing that.

Yes, issue appears resolved today. Thanks for explanation. Confusing how Apple suppoirt had no explanation yestrerday. Now remains to see how Apple Mail transitions to the change. Thanks again...

Confirming that it has auto-fixed itself this morning across all e-mail addresses in our organization.

@Jason_Pelletier's response is an important asterisk, and we're all waiting for an update on this issue, which I have to assume Apple will update Mail to accommodate this, since it'd be unthinkable for them to blatantly abandon a major worldwide e-mail platform that has worked up until now.

Using Safari or Chrome...search "OUTLOOK LOGIN"....respond to required fields...ie EMAIL ID etc....