Question : Contact form on website requires authentication

hi,
   I have a contact form on my website and just recently have been subject to some malicious emails which the police are dealing with, however I still want to use mu online contact form.  Can anyone think of some advanced authentication to make it more difficult for someone to send me something malicious, I am thinking some form of email authentication or when they send a contact us request, we send them an email and they have to click a link to submit the message???

Can anyone help me?

Thanks

Answer : Contact form on website requires authentication

Bad idea...

Have a look here:
http://technet.microsoft.com/en-us/library/bb794745.aspx

You can change the mode of ISA 2006 active / passive in the registry.
If you can make only active FTP, you have to open port 20 to any inbound to the FTP server.