Hi Srinivasa,
Html format provider can be customized such as you can handle an event each time an image should be loaded from URL. Here is some code that demonstrates the approach:
The problem in your case would be to get the image from the Exchange server. You may try doing this via Silverlight WebClient and a separate web-service that would provide the images given the exchange image url. Unfortunately we do not have any experience with such a task.
All the best,
Mike
the Telerik team
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