Autofed is right, if you only use the local loopback IP, it will only allow the server to relay mail from an application hosted on the server, not another machine. If you are testing on a dev machine your mail will not go. You can test whether or not the SMTP server is relaying mail properly by telneting to port 25 on the server. IMPORTANT: You need to do this from the server, not remotely from another machine. Start>Run>Type: telnet yourserver 25 Type: helo this will return Hello and the server ip or server name Next type: mail from: should return "Sender Ok" Next type: rcpt to: should return "Recipient Ok" If this returns as listed above, your SMTP server is relaying mail properly. Keep in mind that when you telnet to port 25 on the server, you will not see the commands as you type. So, 1. Check that SMTP Relay is functioning. 2. Check to see if the machine that is hosting the application has rights to relay mail through the SMTP server. 3. Check your code.