[Zope] Sending attachments

Hi, I've written a form whose contents are emailed with <dtml-sendmail>. It works great, but I want to include a field in the form to select a file which should be included as an attachment in the email. I've used <dtml-mime> and <dtml-boundary> as explained in the manual but it does not work. The resulting email has the *name of the file* as the attachment instead of the file itself! Anyone can help? Thanks Enric