虽然网上有很多类似的DEMO，但是还是整个封装好的例子，，以便以后用；

发送邮箱是直接在web.config配置的。

protected void Button1_Click(object sender, EventArgs e)         {            

string mailto = "843935025@qq.com";            

string mailSubject = "C#邮件测试";            

string mailBody = "C#邮件测试成功";            

string mailFrom = ConfigurationManager.AppSettings["FromMail"];            

if (MySendMail(mailto, mailSubject, mailBody, mailFrom)) {                

　　Error.Text="发送成功！";            

}            

else  {                

　　Error.Text = "发送失败！";            

}        

}

public bool MySendMail(string mailto, string mailsubject, string mailbody, string mailFrom)  {            

try  {                

System.Net.Mail.MailAddress from = new System.Net.Mail.MailAddress(mailFrom);//邮件发送人地址                

System.Net.Mail.MailAddress to = new System.Net.Mail.MailAddress(mailto);//收件人地址                

System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage(from, to);//邮件对象                

message.Subject = mailsubject;                

message.Body = mailbody;                

System.Net.Mail.SmtpClient mySmth = new System.Net.Mail.SmtpClient();//设置服务器                

mySmth.Send(message);//发送邮件                

message.Dispose();                

return true;            

}            

catch             {                 return false;             }        

}

web.config

<appSettings>
    <add key="FromMail" value="wust_chenlei@163.com"/>
  </appSettings>

<system.net>
    <mailSettings>
      <smtp from="Emailname">
        <network host="smtp.163.com" userName="wust_chenlei@163.com" password="cl19911111" port="25" defaultCredentials="false"/>
      </smtp>
    </mailSettings>
  </system.net>