How to optimize Fluent Interface in Web services?

it is my mail class which is a model:

   public class Mail
    {
        public MailService Set { get; set; }
        public string UserName { get; set; }
        public string Password { get; set; }
        public string Subject { get; set; }
        public string Body { get; set; }
        public List Recipients { get; set; }
        public List Bcc { get; set; }
        public List Cc { get; set; }
        public bool Send { get; set; }
        public Mail()
        {
            Set = new MailService(this);
        }

    }

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Also i created a web service which is controller :

namespace MyFluentInterface.Services
{
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]

    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class MailService : System.Web.Services.WebService
    {
          [NonSerialized]
          private readonly Mail _mail;
          public MailService()
          {

          }
          public MailService(Mail mail)
        {
            _mail = mail;
        }

        #region IMail Members

        [WebMethod]
          public MailService UserName(string username)
        {
            _mail.UserName = username;
            return this;
        }
        [WebMethod]
        public MailService Password(string password)
        {
            _mail.Password = password;
            return this;
        }
        [WebMethod]
        public MailService Subject(string subject)
        {
            _mail.Subject = subject;
            return this;
        }
        [WebMethod]
        public MailService Body(string body)
        {
            _mail.Body = body;
            return this;
        }
        [WebMethod]
        public MailService Recipients(List recipients)
        {
            _mail.Recipients = recipients;
            return this;
        }
        [WebMethod]
        public MailService Bcc(List bcc)
        {
            _mail.Bcc = bcc;
            return this;
        }
        [WebMethod]
        public MailService Cc(List Cc)
        {
            _mail.Cc = Cc;
            return this;
        }

        [WebMethod]
        public bool Send()
        {
            _mail.Send = true; // Bir olayin sonucunda bu elde edilmeli
            return true;
        }
        #endregion
    }
}

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Also i have a VIEW project to test:

    public class Test
    {
        private Mail mail { get; set; }
        public Test()
        {
            mail = new Mail();

        }
        public bool Send()
        {
            return mail.Set.Subject("fdsfs").Body("fsdg").Send();
        }
    }

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i utilize from Fluent interface.i used it in web service. But this error returns me:

Cannot serialize member System.ComponentModel.MarshalByValueComponent.Site of type System.ComponentModel.ISite because it is an interface.

How to solve it?