You can use simple telnet command to test mail server function when troubleshootong. This will allow you to connect directly to the server, attempt to send mail and even log the result. Very quick and easy and takes client application issues out of the mix. If you use Telnet on port 25, you can enter the SMTP commands that are used to connect to an SMTP server and send a message exactly as if your Telnet session was an SMTP messaging server. You can see the success or failure of each step in the connection and message submission process.