首先添加命名空间
using System.Net.Mail;

  /// <summary>
        /// 发送邮件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void ForMail(string name, string mail)
        {
            try
            {
                //string email = txtemail.Text.Trim();
                MailAddress MessageFrom = new MailAddress("【发件箱地址】"); //发件人邮箱地址
                string MessageTo = mail; //收件人邮箱地址
                string MessageSubject = bs.HtmlEncode(web_zt.Value.Trim()); //邮件主题  
                string MessageBody = "" + content1.Value.Trim() + ""; //邮件内容 （一般是一个网址链接，生成随机数加验证id参数，点击去网站验证。）";
                if (Send(MessageFrom, MessageTo, MessageSubject, MessageBody))
                {
                    //Response.Write("发送邮件成功");
                }
                else
                {
                    //Response.Write("发送邮件失败");
                }
            }
            catch
            {
                //ClientScript.RegisterStartupScript(ClientScript.GetType(), "myscript", "<script>alert(‘客户信息删除失败‘)</script>");
            }
        }
        /// <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.Normal; //发送邮件的优先等级
            SmtpClient sc = new SmtpClient();
            sc.Host = "smtp.qq.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("【发件箱地址】", "【发件箱密码】"); //指定登录服务器的用户名和密码(发件人的邮箱登陆密码)
            try
            {
                sc.Send(message); //发送邮件
            }
            catch
            {
                return false;
            }
            return true;
        }