Just don't remove the message/notes control from the form. If you've already done that, you'll need to add it back. Look for Message or Notes in the Field Chooser dialog.

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Sue Mosher, Outlook MVP
Author of Microsoft Outlook 2007 Programming:
Jumpstart for Power Users and Administrators
http://www.outlookcode.com/article.aspx?id=54
>I created a new custom outlook form and I need to setup the form to
> allow end users to add attachments when using the form. Is there a
> step-by-step online somewhere?