Cactus, before I open a bug I don't suppose you can tell me an easy way to find out if there's a user defined override?
I've opened three different bugs in the past couple of weeks and every time it's been invalid. 
If it's inline html you are wanting to view then change /etc/e-smith/templates/home/httpd/html/horde/config/mime_drivers.php from false to true.
Test, and if it works, then create a custom-template to preserve your setting.
A user can set in options, mail, message viewing, Block images in HTML messages unless they are specifically requested? and/or Automatically show images in HTML messages when the sender is in my address book?
I am able to view inline images most of the time. There are some issues I have with view certain types of mail with different content types, but I have been to lazy to see if they view fine in OL or TB to file a decent bug report to horde's bugtracker.
If you want to forward me an email you can't view, I could verify that I can either view it or not. Make sure to forward with body text if you do.
John