Send email without Username and Password with Gmail account in ASP.Net

Hi

The below code working fine but I dont want to pass the username and pwd at NetworkCredential. Is there any way to avoid passing username and password ? Is it mandatory that we should pass from username and password in NetworkCredential ?  

SmtpClient _SmtpClient = new SmtpClient("smtp.gmail.com");
            MailAddressCollection _MailAddressCollection = new MailAddressCollection();
            MailMessage _message = new MailMessage();
            _message.From = new MailAddress("abc@gmail.com");
            _message.Body = "Body of the mail";
            _message.Subject = "Sending mail from c# Code";
            _message.To.Add("sat@gmail.com");
            Attachment data = new Attachment("D:\\Attachement.xls");
            _message.Attachments.Add(data);
            _SmtpClient.Port = 587;
            _SmtpClient.Credentials = new System.Net.NetworkCredential("abc@gmail.com", "pwd");
            _SmtpClient.UseDefaultCredentials = true;
            _SmtpClient.EnableSsl = true;
            _SmtpClient.Send(_message);
            System.Console.ForegroundColor = ConsoleColor.Green;
            System.Console.WriteLine("Email Has Been Sent...");
            System.Console.Read();