Exchange att000*.txt attachment

Exchange Server 2003 SP2- Inbound message from senders that have has a confidentiality attachment tacked on (att000*.txt, 426 b) by their server are not delivering. These messages are being forwarded OK to external addresses but not being delivered to mailboxes internally. I have spam filter set to 7-reject. Sender(s) receive no rejection notice. I have added the sender IP to the Global Accept list. How can I allow delivery or find what's blocking them?