I don't think a custom post form is going to work for this purpose, for a couple of reasons:
-- A post form can't be sent by email. It can only be posted to a folder.
-- AFAIK, Sharepoint doesn't know anything about reading custom Outlook properties.
Or have I misunderstood completely how you're using the form? It would be possible to make it work if the post form is just for entering data and it generates a new email message that does not use a custom form and contains all of the necesary information in the message body.
Send form definition: unchecked - Question this seems like a way to
distribute the form. What is the recommended approach to distribute the form
to the posters; we use Exchange?
No, it's a useless setting that does absolutely nothing good in current Outlook versions. See
http://www.outlookcode.com/article.aspx?id=27 for information on distributing forms.
--
Sue Mosher, Outlook MVP
Author of Microsoft Outlook 2007 Programming:
Jumpstart for Power Users and Administrators
http://www.outlookcode.com/article.aspx?id=54