User missing email - tracking results say he got it.

An email from an outside source was sent to a distribution list. There are only three recipients of the distribution list. Two of the recipients got the email. One did not receive the email. This user is using a filter to put all the email sent to that distribution list into a folder. One of the other two recipients is also using a filter, yet he got the email.

The email is nowhere to be found in this recipient's Outlook or in webmail. I did a search of all folders and items using the subject, looked in deleted items and in deleted deleted items, checked the spam folder, and any nearby folders (in case he drug it into something nearby).

The interesting thing is that the server's message tracking results show the events RECEIVE, EXPAND, TRANSFER, and DELIVER with the corresponding sources of SMTP, ROUTING, ROUTING, and STOREDRIVER. The recipient who did not receive the email is listed on each of these records along with the users who did receive the email. I have one Exchange server.

If I export this user's mailbox to a PST file and open it with my Outlook, the email is there. I moved the user's mailbox to another data store and the email still does not show up.

Is there something else I can check to see why this is happening and prevent it from happening in the future?

Thanks!