Are you saying you want to embed the form like Outlook does when you check
send form definition with item checkbox? If so, this would be hard to do
with WebDAV. Eaiest thing is to make sure the folks on the other end have
your custom form and make your message use your custom form message class.
You may run into issues since many servers strip out extra properties, etc.
Plus, you would have to create your own TNEF for the message (Transport
Neutral Encapsulation Format) which is what Exchange uses to package up MAPI
stuff to send over to other servers.
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SharePoint? Check out http://www.yqcomputer.com/