Today I started writing a program to notify me when IP assigned to my router by my broadband provider changes. I wanted this program to check IP address of the router every few minutes and send me email if it detects that IP is changed. For sending email, I used System.Net.Mail.SmtpClient which requires a smtp host. Instead of running a smtp server on my machine, I started looking for free smtp relay servers available on the internet. I was surprised to find out that there are plenty of them available. In fact most of the popular email service providers like windows live, yahoo, gmail offer smtp relay services.