Launching an Outlook Custom Mail Message Form

I have spent hours and hours to make a custom outlook mail message. I
have created an new message type in my VB applications
(objMessage.Type = "IPM.Note.TEST") and it gets sent fine. However,
when the email arrives at the same computer (sending to myself) the
standard Outlook mail form is displayed. My custom form is published
in the Inbox folder as TEST.

My requirement is to launch a custom form when the message type
matches the type sent (IPM.Note.TEST in the example above.

Anyone with any ideas, please help.