MailMessage mail = new MailMessage();
SmtpClient SmtpServer = new SmtpClient(„smtp.gmail.com”);
mail.From = new MailAddress(„your mail@gmail.com”);
mail.To.Add(„to_mail@gmail.com”);
mail.Subject = „Test Mail – 1”;
mail.Body = „mail with attachment”;

System.Net.Mail.Attachment attachment;
attachment = new System.Net.Mail.Attachment(„c:/textfile.txt”);
mail.Attachments.Add(attachment);

SmtpServer.Port = 587;
SmtpServer.Credentials = new System.Net.NetworkCredential(„your mail@gmail.com”, „your password”);
SmtpServer.EnableSsl = true;

SmtpServer.Send(mail);