Good find; however most of those servers are open relays. When you try to send mail through an open relay to a ‘normal’ server, it will scan the server to check if it is an open relay before accepting the message. Here’s the catch; you can sometimes use your ISP’s mail server. The reason for this is that the ISP’s server acts as an open relay to you if the mail is coming from a computer with their own domain, but acts as an ‘authentication-required’ server to the rest of the internet.