Getting null value at web api side when passing as json through asp.net application

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C#

ASP.NET

WebAPI

Code to call web api after passing the Mailmessage class object

MailMessage mail1 = new MailMessage();
mail1.Subject = "Testmail";
mail1.From = new MailAddress("test@gmail.com");
mail1.Body = "Hi, How are you?";
mail1.To.Add("test2@gmail.com");


response = confClient.PostAsJsonAsync("api/Utility/SendMailMessage/0", mail1).Result;

Code in controller of web api to call

public void SendMailMessage(MailMessage mailMessage)
        {
            _smtp = new SmtpClient("mail.gmail.com");
            _smtp.Send(mailMessage);
        }

What I have tried:

I dont know is this because of inbuilt .Net class, I tried in other example passing a student class worked fine. Able to pass values when Namespace System.Web.Mail is used instead of System.Net.Mail for Mailmessage class. I dont want to use System.web.mail.