If you are using turck-mmcache and, in IMP:
* You cannot see any message bodies or attachments OR
* You only see the full text of the headers in the message body
(See http://marc.theaimsgroup.com/?l=imp&m=108163709627707&w=2 for example symptoms)
Go here for instructions on how to fix your problem:
http://marc.theaimsgroup.com/?l=imp&m=108165035111663&w=2
Make sure the cache is deleted everytime Apache is restarted: