Man I wish I had the answer, doesn't it suck that OE is so much more capable
in this area?  And message properties too, OE lets you view the raw source
as sent via SMTP, while Outlook only lets you view the routing headers...
bums me out every time I think about it.

There is a sleazy way to work around it, won't give you all of the
functionality (like color-coded keywords in HTML source, etc.) but may be of
some use:

0. Download/install Outlook Redemption
1. Open the VBA editor from inside of OL
2. Create a form (I'll call it SourceEditorForm) with one control, a text
input (I'll call it HTMLSource.)
3. Add 2 event handlers as shown below

   Private Sub UserForm_Initialize()
       HTMLSource.Text = buf
   End Sub

   Private Sub UserForm_QueryClose(Cancel As Integer, CloseMode As Integer)
       buf = HTMLSource.Text
   End Sub

4. Create a macro, and add the following global variable declaration and
function [which will be called by the macro] to the module:

Public buf As String

Sub EditHTMLSource()
   Dim oSafeItem As Object
   Set oSafeItem = CreateObject("Redemption.SafeMailItem")
   oSafeItem.Item = Application.ActiveInspector.CurrentItem
   Load SourceEditorForm

   buf = oSafeItem.HTMLBody
   SourceEditorForm.Show vbModal
   oSafeItem.HTMLBody = buf

   Unload SourceEditorForm
   Set oSafeItem = Nothing
End Sub

5. Create a custom button in the message composer window to call the macro

To be sure this lacks a lot of things, it needs to make sure the message is
HTML, should check for empty strings, should make sure oSafeItem isn't
nothing -- should really probably oughta be an AddIn... but what the hell?

-Mark