I wonder -- would it be possible to convert the base 64 from the file attachment control and specify that as the attachment for the email? Actually, I just went to MSDN to look at the Add method for Attachments, and it seems to want a path. BUT, since your form is going to have to be full trust anyway, if you are going to access the user's file system, you could decode the base 64 and save the file to a temp location and pick it up from there -- clean up the file you saved after sending the email. The base 64 in the file attachment control, to my knowledge, doesn't contain the file path.