Emails are not going


I have installed the plugin in my wordpress 3.0 version with network active. This is hosted on a windows server with IIS webserver.

I have created the rules for auto followup but the mails are not going. I tested several times with different email ids but no email is sent on sign up.

How does this plugin sends email. I mean which email program it uses..? Do i need to change some SMTP settings etc..?