SMTP Event sink

Hi

I have win2k srv sp4 with iis & smtp services installed, I have developed an
c# com class using SMTPEventSink to intercept some e-mail messages.
I have registered the com class using SMTPReg.vbs, but when I try to send a
new mail message using the smtp, the event sink class is initialized
correctly, but the event OnArrival is never call.
How do I to solve this problem?

Thanks is advance to all.

Simon.