代码如下：

using System.Net.Mail;

protected void Page_Load(object sender, EventArgs e)
    {
        MailAddress MessageFrom = new MailAddress("zhangxinpingit@sina.com");   //发件人邮箱地址
        string MessageTo = "zhangxinpingit@163.com";   //收件人邮箱地址
        string MessageSubject = "邮件主题";         //邮件主题
        string MessageBody = "这里是邮件内容。";    //邮件内容
        if (Send(MessageFrom, MessageTo, MessageSubject, MessageBody))
        {
            Response.Write("发送邮件成功");
        }
        else
        {
            Response.Write("发送邮件失败");
        }
    }
    /// <summary>
    /// 发送电子邮件
    /// </summary>
    /// <param name="MessageFrom">发件人邮箱地址</param>
    /// <param name="MessageTo">收件人邮箱地址</param>
    /// <param name="MessageSubject">邮件主题</param>
    /// <param name="MessageBody">邮件内容</param>
    /// <returns></returns>
    public bool Send(MailAddress MessageFrom, string MessageTo, string MessageSubject, string MessageBody)
    {
        MailMessage message = new MailMessage();

        message.From = MessageFrom;
        message.To.Add(MessageTo);              //收件人邮箱地址可以是多个以实现群发
        message.Subject = MessageSubject;
        message.Body = MessageBody;
        message.IsBodyHtml = true;              //是否为html格式
        message.Priority = MailPriority.High;   //发送邮件的优先等级

        SmtpClient sc = new SmtpClient();
        sc.Host = "smtp.sina.com";              //指定发送邮件的服务器地址或IP
        sc.Port = 25;                           //指定发送邮件端口
        sc.Credentials = new System.Net.NetworkCredential("zhangxinpingit@sina.com", "zhangxinping"); //指定登录服务器的用户名和密码
        try
        {
            sc.Send(message);       //发送邮件
        }
        catch
        {
            return false;
        }
        return true;
    }