Submit button fails to submit via Outlook

I have created a PDF form with a Submit button feature in Acrobat 8.

Everything works fine except the submission itself. In my own testing the email message is set up in Outlook (2003) and the attachment shows as attached (either the complete PDF document or the datafile, depending on what I've selected). However, the message does not send. There is simply the Outlook grey bar across the top that says "this message has not been sent". I anticipate this is a problem with Microsoft Outlook, but does anyone know what is happening?

To send the file a different way, I can open an Outlook email message and then attach the file and send it, but this defeats the purpose of a submit button in the form itself.

Thanks for your help and apologies if this question has already been asked and answered. I'm new to the forum. Many thanks for your guidance.