Microsoft is reporting on a new issue affected users of Exchange Server.
Users are reporting that their legitimate email is ending up in their Junk mail folder.
The issue appears to be affecting mainly North American users, and have been ongoing for around 40 minutes now.
Microsoft says they are reviewing diagnostic data to better understand the issue in order to isolate and address the source of the problem.
Update: Microsoft has identified that a recent change has resulted in an issue in which inbound email is being incorrectly routed to the junk folder. They are working to revert the change to mitigate impact.
In the meantime, if you are missing some important email you were expecting, you now know where to check.