I am seeing this same issue on Win XP. I have confirmed that Outlook Express works with smtp.gmail.com to send emails, but the Silence Detector simply either hangs for a minute and posts the "Connection timed out" message, or hangs forever and I have to restart Silence Detector.
If I attempt to specify the port (example: smtp.gmail.com:465), then that hangs the Silence Detector software as well. Furthermore, I have tried it with Windows Firewall on and off, and also specifying an "Exception" for SD in Windows Firewall. The program never sends the email in any of these scenarios.
Is there a way to get a better event log of what happened at the time of the error?