If you have issues in connecting to your office 365 mailbox through your outlook, or some of the users complaining issues with their outlook, then you are not alone.
Seems there are few customers affected with Exchange online services, Microsoft is working on it.
Update – Although the issue is now completely resolved
If you have issues with Azure MFA, then you are likely affected due to issue caused by Microsoft. Please check your message center in office 365 to confirm or call Microsoft.
This has been resolved completely. If you still face issues then it’s time to log it with Microsoft
We are back with MFA issue again. MS is working