Mail Not Read vs. Mail Not Filed:
Mail Not Filed emails will show under all users as they are unable to be filed and associated with an existing Activity/Issue.
Mail Not Read will show under an assigned user due to being associated with an existing Activity/Issue which has an Assigned User.
Example: If you receive a phone call from a customer stating they have sent an email.
When the customer calls and you have reviewed your home page and are not seeing any incoming emails.
The best way to review/troubleshoot is to verify under Admin > Settings & Utilities > Mail Retrieval. Here you can verify the last time a mail retrieval processed (and clear any errors if you have reached an error count of 10).
Then once you have verified that your email sync has recently processed you can look under Inquires > By User > Mail for the incoming message (or look under Inquiries > By User > Action Summary to see if another user in the system received the message).