ChkIP used to available under the name IP Mailer, but when the product was totally rewritten and re-designed in 2012 to be a product in the cloud, it was renamed as well. Welcome to the new and improved IP Mailer (originally launched in 2001).
"IP Mailer 2004" stopped resolving external IP addreses on January 21st 2013. The IP Mailer Windows application, at the time it was disabled, resolved an external IP address for customers once every 2 seconds or less. The IP Mailer server received over 29 million requests for external IP address per year!
That is all you need to do. After the above steps, your computer is monitored and you will recieve emails when the IP address changes.