Thanks for your reply.
Your book was very helpful.
I have tried the form regions (and without your book, I would not have been able to do it), but the GUI can not be what the users are expecting.
I would have been pleased that the Reading Pane simply displays the standard mail fields of my custom form. That would have been enough for my purpose. But it does not work.
I dug further since yesterday and I think I did not take enough attention to the fact that the VBA compiler provided with Outlook may not suffice and that I have to install Visual Studio 2005, perhaps with a few extra libraries, not sure which ones yet. Why is it so, I do not know.
At first when I tried to build my custom form, I tried to make it entirely using VBA, but I ran into trouble with some functions that did not worked, so I switched to VBScript which worked nicely, but with the reading pane, but with RMS. The reading pane issue, I already explained it. With RMS, I do not know why, but VBScript Custom form + RMS implies that the received message appears with the RMS-protected content as an attachment, and not directly in the body of the mail. See the attached picture.
I suppose that Outlook get lost when a message.rpmsg is embedded within a winmail.dat file. And I am not sure that developing a VBA add-in will solve this issue. I have asked Microsoft, but I have got not any answer so far. Any idea?

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