In the new version of IMP (as of 05/08/03) there is an issue where the messages listed in the "Sent Items" folder will only display the address the messages were sent from (usually all the same address).
This will occur if the email address the messagess were sent from does not match the email address set in the default identity.
The simplest solution is to simply click on a message to view the original message :). To prevent this altogether, use the below solution
Make sure the email address listed in the "Default Identity" in webmail matches the "From:" address listed in the "Sent items" folder. You can find the identity settings by doing the following:
1. Log into webmail
2. Click "Options"
3. Click "Personal Information"
4. Select the default identity and click "Edit your identities"
5. Verrify the email address field, and be sure the correct "Sent mail folder" is selected