I have had this happen 3 times today. This is the first day it has happened...
I have had instances of external email addressed to specific internal users being sent to multiple users mailboxes. For example, an email was sent from an outside source to our exchange server to email@example.com. That email was then delivered to multiple peoples mailboxes in our internal network. It's like the email was routed to many Distribution Lists instead of the specific user. Everyone on our network did not receive it, just all people in various departments
Like I said, this has happened 3 times today from different external addresses to different internal email addresses.