Restore Microsoft 365 Email Access

My Microsoft 365 email suddenly stopped working on my phone’s mail app. When I try to check messages I simply get a generic “not working” notice—no clear Invalid Credentials or Account Locked prompt, just an endless failure to sync. I still use the same password and haven’t changed any settings, so I suspect something has shifted at the Microsoft 365 side, whether it’s a security flag, an expired token, or a service configuration that needs attention.

Here’s what I need from you:
• Investigate why mobile email access has broken and pinpoint the root cause—credential issue, licence problem, mailbox corruption, or anything that might surface in the admin centre or Azure AD logs.
• Guide me through or perform the appropriate fix so I can send and receive mail again on my mobile app.
• Confirm the solution by successfully syncing mail on the device and showing that new test messages flow in both directions.

You should be comfortable with Microsoft 365 admin tools, Exchange Online diagnostics, and mobile-client troubleshooting (iOS and Android). Once we’re done I expect to be back to normal email use, with any policy changes documented so I can avoid the same outage in future.