public class Email
{
    public Email()
    {
    }

    /// <summary>
    /// 发送邮件
    /// </summary>
    /// <param name="to">收件人邮件地址</param>
    /// <param name="from">发件人邮件地址</param>
    /// <param name="subject">邮件主题</param>
    /// <param name="body">邮件内容</param>
    /// <param name="userName">登录smtp主机时用到的用户名,注意是邮件地址'@'以前的部分</param>
    /// <param name="password">登录smtp主机时用到的用户密码</param>
    /// <param name="smtpHost">发送邮件用到的smtp主机</param>
    public static void Send(string to, string from, string subject, string body, string userName, string password, string smtpHost)
    {
        MailAddress from1 = new MailAddress(from);
        MailAddress to1 = new MailAddress(to);
        MailMessage message = new MailMessage(from1, to1);
        message.Subject = subject; //设置邮件主题 
        message.IsBodyHtml = true; //设置邮件正文为html格式 
        message.Body = body; //设置邮件内容 
        SmtpClient client = new SmtpClient(smtpHost);
        //设置发送邮件身份验证方式 
        //注意如果发件人地址是abc@def.com，则用户名是abc而不是abc@def.com 
        client.Credentials = new NetworkCredential(userName, password);
        client.Send(message);
    } 

}

------解决方案--------------------
调用方法
C# code
protected void Button1_Click(object sender, EventArgs e)
    {
        Email.Send("duanshuo@126.com", "duanshuo@126.com", "测试", "<font color='red'>邮件测试，呵呵</font>", "duanshuo", "86260841", "smtp.126.com");

        Page.ClientScript.RegisterStartupScript (Page .GetType (),"","<script>alert('发送成功！')</script>");
    }

------解决方案--------------------
     System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage();
       message.From = new System.Net.Mail.MailAddress(TextBox3.Text);//发送人邮箱地址，与smtp节点中的from值一致
       message.To.Add(new System.Net.Mail.MailAddress("11898468@qq.com"));    //接收人邮箱地址
       message.To.Add(new System.Net.Mail.MailAddress("yangchen163@sina.com")); //多个收件人邮箱地址
       message.Subject = TextBox1.Text;
       message.Body = TextBox2.Text;
       message.IsBodyHtml = true;
       System.Net.Mail.SmtpClient smtpclient = new System.Net.Mail.SmtpClient("smtp.qq.com", 25);
       smtpclient.Credentials = new System.Net.NetworkCredential(TextBox3.Text, "huahuaaiyangchen");//参数分别是邮箱用户名和密码
       try
       {
           smtpclient.Send(message);
           Response.Write("成功");
       }
       catch
       {
           Response.Write("失败");
       }

我用QQ邮箱测试过



------解决方案--------------------
http://blog.csdn.net/dongdongleng/archive/2010/08/28/5845124.aspx

看看这个

------解决方案--------------------
探讨


C# code
public class Email
{
    public Email()
    {
    }

    /// <summary>
    /// 发送邮件
    /// </summary>
    /// <param name="to">收件人邮件地址</param>
    /// <param name="from">发件人邮件地址</param>