how can i send an email to an exchange email in asp.net?

I have a feedback page. But i can not program to send a reply mail to an exchange email. Any one help me?

SmtpClient smtpClient = new SmtpClient();
            MailMessage message = new MailMessage();            
 
            try
            {
                MailAddress fromAddress = new MailAddress("acb@email.com");
                smtpClient.Host = "localhost";
                smtpClient.Port = 25;
                message.From = fromAddress;
                Email send to
                message.To.Add("def@def.com");//this is an exchange account
                message.Subject = txtTitle.Text;
                message.IsBodyHtml = false;
                message.Body = txtDescription.Text;
                smtpClient.Send(message);
          }
            catch (Exception ex)
            {
                
            }

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