This is from the Chattermail Site's FAQs:
I'm Not Seeing Attachments That Are Sent To Me

There are a few common reasons for this...
If your senders use a Microsoft Exchange server, it's most likely that your senders are sending in Microsoft's internal format (which can be turned off in Outlook). No other applications can see them in this format.
Another possibility is that they are being sent from a Mac, in which case the mail program needs to be told to use windows-friendly attachments.
If you can't figure out the problem, please send us a log showing the LOADING of a message that should have attachments (but doesn't), following the instructions in the FAQ regarding logging.