I have installed and configured Gateway IP Monitor v1.4 on XP Pro SP3. I have sent the test email and receive the response in my Inbox.
I've enabled the Regular Notification option and set the interval to 5 minutes but don't receive any messages. There are no error messages in the Event Log. The Gateway IP Monitor service is running and I've re-installed the software but still don't receive any regular notifications.
Can you take a look at the "Application Event Log", to see if there are any errors or warnings reported by Gateway IP Monitor? If it can't send an email, then it would log an error there.
Also, are you receiving emails when the IP address changes?