Dynamic create file and send in mail without save a file on server

StringBuilder messagebody1 = new StringBuilder();
            messagebody1.Append("Category,Product,First Name,Last Name,EmailId,Phone number,Location,PinCode,Message" + System.Environment.NewLine);
            messagebody1.Append(Category + "," + Product + "," + firstName + "," + lastName + "," + emailId + "," + phoneNumber + "," + location + "," + pincode + "," + queryText + System.Environment.NewLine);
            StringBuilder messagebody = new StringBuilder();
            messagebody.Append("Category:" + Category + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("Product:" + Product + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("First Name: " + firstName + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("Last Name: " + lastName + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("EmailId:" + emailId + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("Phone number:" + phoneNumber + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("Location:" + location + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("PinCode:" + pincode + System.Environment.NewLine + System.Environment.NewLine);
            messagebody.Append("Message:" + queryText + System.Environment.NewLine + System.Environment.NewLine);



            MemoryStream stream = new MemoryStream(Encoding.ASCII.GetBytes(messagebody1.ToString()));
            string to = "pramod.koli1@gmail.com";
            string from = ConfigurationManager.AppSettings["QueryEmail"].ToString();
            string subject = "Leave a query:" + category + "-" + product;
            string body = messagebody.ToString();
            SmtpClient SMTPServer = new SmtpClient("*********");
            MailMessage mailObj = new MailMessage(from, to, subject, body);
            mailObj.Attachments.Add(new Attachment(stream, "details.csv", "text/csv"));
           // mailObj.IsBodyHtml = true;
            SMTPServer.Send(mailObj);