WinForm窗体代码如下：

<span style="font-size:14px;">using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
<span style="color:#ff0000;">//要添加的引用如下</span>
using System.Net.Mail;
using System.Net.Mime;
using System.Timers;
using System.IO;

namespace NovelCS {
    public partial class Form3 : Form {
        public Form3() {
            InitializeComponent();
        }
           
        private void Form3_Load(object sender, EventArgs e) {
            //一些常见的发送邮件服务器地址 一般都是 stmp.**.com   **=qq 或 126 或163 或 gmail 有例外的，具体问度娘

            string senderServerIp = "smtp.qq.com";           
            string toMailAddress = "1449740504@qq.com";
            string fromMailAddress = "1449740504@qq.com";
            string subjectInfo = "My First Email";
            string bodyInfo =@"Hello Jackerson, \r\n
                                        This is my first testing e_mail.But what all thess is from  an author named Eric Sun.
                                        Thank you,Eric Sun.";
            string mailUsername = "1449740504";
            string mailPassword = "******"; //发送人邮箱的密码
            string mailPort = "25";   //邮箱端口号
            string attachPath = "D:\\jsj.txt; D:\\jsj2.txt";//附件本地地址

            MyEmail email = new MyEmail(senderServerIp, toMailAddress, fromMailAddress, subjectInfo, bodyInfo, mailUsername, mailPassword, mailPort, false, false);
            email.AddAttachments(attachPath);
            email.Send();
        }
               
    }

    public class MyEmail {
        private MailMessage me;//主要处理发送邮件的内容，例：收发件人地址、标题、主体、图片
        private SmtpClient sc;   //主要处理用smtp发送邮件的配置信息，例：发送邮件服务器地址、发送端口号、验证方式
        private int mSenderPort;                         //发送邮件所用的端口号（htmp协议默认为25）
        private string mSenderServerHost;          //发件箱的邮件服务器地址（IP形式或字符串形式均可）
        private string mSenderUserName;           //发件箱的用户名（即@符号前面的字符串，例如：hello@163.com，用户名为：hello）
        private string mSenderPassword;             //发件箱的密码
        private bool mEnableSsl;                         //是否对邮件内容进行socket层加密传输
        private bool mEnablePwdAuthentication;  //是否对发件人邮箱进行密码验证

        ///<summary>
        /// <strong><span style="color:#ff0000;">构造函数</span></strong>
        ///</summary>
        ///<param name="server">发件箱的邮件服务器地址</param>
        ///<param name="toMail">收件人地址（可以是多个收件人，程序中是以“;"进行区分的）</param>
        ///<param name="fromMail">发件人地址</param>
        ///<param name="subject">邮件标题</param>
        ///<param name="emailBody">邮件内容（可以以html格式进行设计）</param>
        ///<param name="username">发件箱的用户名（即@符号前面的字符串，例如：hello@163.com，用户名为：hello）</param>
        ///<param name="password">发件人邮箱密码</param>
        ///<param name="port">发送邮件所用的端口号（htmp协议默认为25）</param>
        ///<param name="sslEnable">true表示对邮件内容进行socket层加密传输，false表示不加密</param>
        ///<param name="pwdCheckEnable">true表示对发件人邮箱进行密码验证，false表示不对发件人邮箱进行密码验证</param>
        public MyEmail(string server, string toMailAddress, string fromMailAddress, string emailTitle, string emailBody, string username, string password, string port, bool sslEnable, bool pwdCheckEnable) {
            try {
                me = new MailMessage();
                me.To.Add(toMailAddress);
                me.From = new MailAddress(fromMailAddress);
                me.Subject = emailTitle;
                me.Body = emailBody;
                me.IsBodyHtml = true;
                me.BodyEncoding = System.Text.Encoding.UTF8;
                me.Priority = MailPriority.Normal;
                this.mSenderServerHost = server;
                this.mSenderUserName = username;
                this.mSenderPassword = password;
                this.mSenderPort = Convert.ToInt32(port);
                this.mEnableSsl = sslEnable;
                this.mEnablePwdAuthentication = pwdCheckEnable;
            } catch (Exception ex) {
                MessageBox.Show(ex.ToString());
            }
        }

        ///<summary>
        /// <strong><span style="color:#ff0000;">添加附件</span></strong>
        ///</summary>
        ///<param name="attachmentsPath">附件的路径集合，以分号分隔</param>
        public void AddAttachments(string attachmentsPath) {
            try {
                string[] path = attachmentsPath.Split(';'); //以什么符号分隔可以自定义
                Attachment data;
                ContentDisposition disposition;
                for (int i = 0; i < path.Length; i++) {
                    data = http://www.mamicode.com/new Attachment(path[i], MediaTypeNames.Application.Octet);>
备注：
(1)经过测试，确实可以使用。
(2)本文出处：Eric Sun(http://www.cnblogs.com/mingmingruyuedlut/archive/2011/10/14/2212255.html)
c# 发送邮件、附件