Build file without storing to the hard drive then add it as attachment

How to make a file and place it as an attachment in an e-mail? My problem is how to build the CVS file. It would be great if it was possible to build it without saving anything to the hard drive.

This is how I send the e-mail.

    public void SendMail()
    {
        try
        {
            MailMessage mail2 = new MailMessage();
            mail2.To.Add("aahsdkjahsd@yahoo.com");
            mail2.From = new MailAddress(TxtEpost.Text, TxtEtternavnForrnavn.Text, System.Text.Encoding.UTF8);

            mail2.Subject = "Bestille katalog";
            mail2.SubjectEncoding = System.Text.Encoding.UTF8;

           
           
            Attachment atch = new Attachment("MyFile.CVS");
            mail2.Attachments.Add(atch);
           
            mail2.Body = "";

            mail2.BodyEncoding = System.Text.Encoding.UTF8;
            mail2.IsBodyHtml = false;
            mail2.Priority = MailPriority.High;
            //Add the Creddentials
            SmtpClient client2 = new SmtpClient();
            //For secure SMTP remove comments.....
            //client2.Credentials = new System.Net.NetworkCredential("jakslajsd@gmail.com", "password");
            //client2.Port = 587;//or use 587, 465
            client2.Host = "smtp.jaslkdj.com";
            //client2.EnableSsl = true;
            //client.SendCompleted += new SendCompletedEventHandler(client_SendCompleted);
            client2.Send(mail);
        }
        catch (Exception ex)
        {
            //Label1.Text += ex.ToString();
        }