We are looking into some spam that was received last night and are curious as to how it got around our network.
The email is a plain text message with what I assume is a fake From: address, the intersting part about this spam though is the recipient, Mail-User@ourdomain.com. We don't have a mailbox or DL using this account but the mail was still received by about 50 users that we know of.
I've tried to sending a message to Mail-User@ourdomain.com but it comes back as not valid. Can anyone explain how this got to our users mailboxes?
We are using Exchange 5.5 SP4