see
SMTP server and email FAQ
http://www.asp.net/Forums/ShowPost.aspx?tabindex=1&PostID=268037
The transport failed to connect to the server
1) The server specified in the SmtpServer property is not valid. 2) The SMTP server requires authentication to relay email. The ASP.NET mail classes do not allow you to include authentication information. If you are working with a local SMTP server, you might be able to configure the server so that it does not require authentication for a local relay (127.0.0.1).
SMTP server and email FAQ
http://www.asp.net/Forums/ShowPost.aspx?tabindex=1&PostID=268037
The transport failed to connect to the server
1) The server specified in the SmtpServer property is not valid. 2) The SMTP server requires authentication to relay email. The ASP.NET mail classes do not allow you to include authentication information. If you are working with a local SMTP server, you might be able to configure the server so that it does not require authentication for a local relay (127.0.0.1).
If you use a SMTP server in the LAN , yes , you can send mail
But if you use a SMTP server in WWW , you have to get a accounts and the password to key this accounts