All you need to do is to the following
1. Set up a database table with 3 columns (Hash,Filename,Notify)
2. The hash will be a unique md5 hash generated from say a unix date
3. the notify column is the email address of the user to notify
create a public visible website and create the file Download.aspx
the link you would give would read something like
http://www.website.com/download.aspx?hash=A7BCD6E67F....
....
your download.aspx file will look into the database to filnd the filename and email address that corresponds to the hash
if a hash is found send an email to the notify address and then use response.transmitfile the continue the download
Done