> What I was thinking is using mailto: to create a complete mail on a client
without an attachment and then when a user sends email reroute it to a
server for a file attachment and forwarding.
Mail is sent to an SMTP server, not an application server. ASP has no way
to know that mail is being sent anywhere. You can only "intercept" mail
before it is sent along this way... e.g. if you generate the e-mail from the
server side.
mailto: is a very unreliable method, by the way. Some people don't have a
default mail reader defined, some people have default mail readers that
don't support mailto:, a few will modify the form contents and change the
destination and several other attributes, and the rest can choose to just
close the mail window and nothing gets sent at all