//using System.Net;
//using System.Net.Mail;
//using System.Text;

//电子邮件
MailMessage mailMessage = new MailMessage();
mailMessage.From = new MailAddress("111111@qq.com", "张三");//发件人
mailMessage.To.Add(new MailAddress("222222@qq.com", "李四"));//收件人
mailMessage.To.Add(new MailAddress("333333@qq.com", "王五"));//收件人
mailMessage.CC.Add(new MailAddress("444444@qq.com", "小二"));//抄送人
mailMessage.Priority = MailPriority.Normal;//优先级
mailMessage.SubjectEncoding = Encoding.UTF8;
mailMessage.Subject = "Happy New Year!";//标题
mailMessage.BodyEncoding = Encoding.UTF8;
mailMessage.IsBodyHtml = true;
mailMessage.Body = "<font color=red>Hello,Happy New Year!</font>";//内容
mailMessage.Attachments.Add(new Attachment(@"F:\Me.jpg"));//附件

//邮件服务器
SmtpClient smtpClient = new SmtpClient();
smtpClient.Host = "smtp服务器地址";
smtpClient.Credentials = new NetworkCredential("用户名", "用户密码");
smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
smtpClient.Send(mailMessage);

smtpClient.EnableSsl = true;
smtpClient.UseDefaultCredentials = false;
smtpClient.Credentials = new NetworkCredential("用户名", "申请的授权码");