MailAddress from = new MailAddress("070812041@163.com", "东东");          //邮件的发件人,后面为显示的名字
            MailMessage mail = new MailMessage();           
            mail.Subject = txtSubject.Text;                                            //设置邮件的标题
            mail.From = from;                                                          //设置邮件的发件人
            
            //多人发送
            string address = "";
            string displayName = "";         
            string[] mailNames = (txtMailTo.Text + ";").Split(';');
            foreach (string name in mailNames)
            {
                if (name != string.Empty)
                {
                    if (name.IndexOf('<') > 0)
                    {
                        displayName = name.Substring(0, name.IndexOf('<'));
                        address = name.Substring(name.IndexOf('<') + 1).Replace('>', ' ');
                    }
                    else
                    {
                        displayName = string.Empty;
                        address = name.Substring(name.IndexOf('<') + 1).Replace('>', ' ');
                    }
                 //   mail.To.Add(new MailAddress(address, displayName));
                    mail.CC.Add(new MailAddress(address, displayName));                //收件人地址的集合
                }
           
            }
            
            mail.Body = txtBody.Text;                                                  //设置邮件的内容            
            mail.BodyEncoding = System.Text.Encoding.UTF8;                             //设置邮件的格式
            mail.IsBodyHtml = true;                                                    //设置正文是否为HTML格式
            mail.Priority = MailPriority.Normal;                                       //设置邮件的发送级别
            if (txtMailTo.Text != "")
            {
            string fileName = txtUpFile.Text.Trim();                                   //设置邮件的附件
            fileName = fileName.Substring(fileName.LastIndexOf("\\") + 1);             //取文件名
            mail.Attachments.Add(new Attachment(fileName));                            //添加附件到邮件当中
            }
            mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnSuccess;
            SmtpClient client = new SmtpClient();
            client.Host = "smtp.163.com";                                              //设置SMTP的地址，注意：是什么邮箱就应该用相对应的地址          
            client.Port = 25;                                                          //设置用于 SMTP 事务的端口，默认的是 25
            client.UseDefaultCredentials = false;       
            client.Credentials = new System.Net.NetworkCredential("*****", "*****");//我的邮箱的登录名和密码。就是发送方的用户名和密码，要对应上面的Host地址
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            
            client.Send(mail);                                                         //邮件的正式发送
            MessageBox.Show("发送成功");                    
        }

        private void btn_send_Click(object sender, EventArgs e)
        {
            sendMail();
        }

------解决方案--------------------
图片也可作为附件发送 
  
MailMessage message = new MailMessage(From, To, Subject, Body);
 Attachment data = null;
 if (Files != null && Files.Length > 0)
 {
 foreach (string file in Files)