Sending Attachments Through W2K3 SMTP Virtual Server

My users are using the SMTP virutal server piece of IIS6 to send email
out. Everything is working fine, apart from sending certain types of
attachments. I have no problem sending *.doc, *.wav, *.pdf, but when I
try to send an attachement with a generic extension say *.dsy or no
extension at all, the message never gets through.

Any ideas?

.

Loading