在KS系统中有个发送邮件的功能需要做上网查阅资料以后，通过自己的部分修改实现了发送邮件的功能话不多说先来个界面：

邮件发送分一下步骤：

1.smtp服务信息设置

2.验证发件人信息

3.添加附件

4.正式发送邮件

5.发送邮件后处理

1.smtp服务信息设置

   #region 设置Ｓmtp服务器信息

        /// <summary>

        /// 设置Ｓmtp服务器信息

        /// </summary>

        /// <param name="ServerName">SMTP服务名</param>

        /// <param name="Port">端口号</param>

        private void setSmtpClient(string ServerHost, int Port)

        {

            SmtpClient = new SmtpClient();

            SmtpClient.Host = ServerHost;//指定SMTP服务名  例如QQ邮箱为 smtp.qq.com 新浪cn邮箱为 smtp.sina.cn等

            SmtpClient.Port = Port; //指定端口号

            SmtpClient.Timeout = 0;  //超时时间

        }

        #endregion

2.验证发件人信息

        #region 验证发件人信息

        /// <summary>

        /// 验证发件人信息

        /// </summary>

        /// <param name="MailAddress">发件邮箱地址</param>

        /// <param name="MailPwd">邮箱密码</param>

        private void setAddressform(string MailAddress, string MailPwd)

        {

            //创建服务器认证

            NetworkCredential NetworkCredential_my = new NetworkCredential(MailAddress, MailPwd);

            //实例化发件人地址

            MailAddress_from = new System.Net.Mail.MailAddress(MailAddress, textBoxX4.Text);

            //指定发件人信息  包括邮箱地址和邮箱密码

            SmtpClient.Credentials = new System.Net.NetworkCredential(MailAddress_from.Address, MailPwd);

            ;

        }

        #endregion

3.添加附件

  #region 检测附件大小

        private bool Attachment_MaiInit(string path)

        {

            try

            {

                FileStream_my = new FileStream(path, FileMode.Open);

                string name = FileStream_my.Name;

                int size = (int)(FileStream_my.Length / 1024 / 1024);

                FileStream_my.Close();

                //控制文件大小不大于10Ｍ

                if (size > 10)

                {

                    MessageBox.Show("文件长度不能大于10M！你选择的文件大小为" + size.ToString() + "M", "警告", MessageBoxButtons.OK, MessageBoxIcon.Warning);

                    return false;

                }

                return true;

            }

            catch (IOException E)

            {

                MessageBox.Show(E.Message);

                return false;

            }

        }

        #endregion

4.正式发送邮件

        private void btnSend_Click_1(object sender, EventArgs e)

        {

            if (txt_SmtpServer.Text == "")

            {

                MessageBox.Show("请输入SMTP服务器名！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);

                return;

            }

            if (textBoxX2.Text == "")

            {

                MessageBox.Show("请输入发件人邮箱地址！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);

                return;

            }

            if (txtformPwd.Text == "")

            {

                MessageBox.Show("请输入发件人邮箱密码！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);

                return;

            }

            if (MessageBox.Show("您确定要发送当前邮件吗？", "询问", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) == DialogResult.OK)

            {

                try

                {

                    //初始化Ｓmtp服务器信息

                    setSmtpClient("smtp." + txt_SmtpServer.Text.Trim() + comboBoxEx3.Text, Convert.ToInt32(numericUpDown1.Text));

                }

                catch (Exception Ex)

                {

                    MessageBox.Show("邮件发送失败,请确定SMTP服务名是否正确！" + "\n" + "技术信息:\n" + Ex.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);

                    return;

                }

                try

                {

                    //验证发件邮箱地址和密码

                    setAddressform(textBoxX2.Text.Trim() + comboBoxEx2.Text, txtformPwd.Text.Trim());

                }

                catch (Exception Ex)

                {

                    MessageBox.Show("邮件发送失败,请确定发件邮箱地址和密码的正确性！" + "\n" + "技术信息:\n" + Ex.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);

                    return;

                }

                //清空历史发送信息 以防发送时收件人收到的错误信息(收件人列表会不断重复)

                MailMessage_Mai = new MailMessage();

                MailMessage_Mai.To.Clear();

                //添加收件人邮箱地址

                MailAddress_to = new MailAddress(textBox4.Text.Trim() + comboBox4.Text.Trim());

                MailMessage_Mai.To.Add(MailAddress_to);

                //发件人邮箱

                MailMessage_Mai.From = MailAddress_from;

                //邮件主题

                MailMessage_Mai.Subject = txttitle.Text;

                MailMessage_Mai.SubjectEncoding = System.Text.Encoding.UTF8;

                //邮件正文

                MailMessage_Mai.Body = Rtb_Message.Text;

                MailMessage_Mai.BodyEncoding = System.Text.Encoding.UTF8;

                //清空历史附件  以防附件重复发送

                MailMessage_Mai.Attachments.Clear();

                //注册邮件发送完毕后的处理事件

                SmtpClient.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);

                //开始发送邮件

                SmtpClient.SendAsync(MailMessage_Mai, "000000000");

            }

        }

5.发送邮件后处理

 #region 发送邮件后所处理的函数

        private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)

        {

            try

            {

                if (e.Cancelled)

                {

                    MessageBox.Show("发送已取消！");

                }

                if (e.Error != null)

                {

                    MessageBox.Show("邮件发送失败！" + "\n" + "技术信息:\n" + e.ToString(), "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);

                }

                else

                {

                    MessageBox.Show("邮件成功发出!", "恭喜!", MessageBoxButtons.OK, MessageBoxIcon.Information);

                }

            }

            catch (Exception Ex)

            {

                MessageBox.Show("邮件发送失败！" + "\n" + "技术信息:\n" + Ex.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);

            }

        }

        #endregion

参考资料连接：http://www.cnblogs.com/maiweibiao/articles/1837821.html

代码：http://download.csdn.net/detail/gwblue/6353807