(Step 1: download the free curl green software and unzip it to the specified directory. Step 2: visit the website that looks up the local IP address through curl command line mode, and get the local IP address from the returned web page content. Step 3: compare the IP address obtained this time with the IP address saved last time. If there is no change, no email will be sent. Step 4: if the IP address has changed this time, call curl to send mail.)