1 Failed to load http://example.com/sendemail: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://dev.example.com' is therefore not allowed access.
2. XHR finished loading: OPTIONS "http://example.com/sendemail".

$.ajax({
    type: "POST",
    url: "http://example.com/sendemail",
    data: JSON.stringify(data),
    dataType : "json",
    contentType: "application/json; charset=utf-8",
    success: function(data){
      console.log('success');
    },
    failure: function(errMsg) {
        console.log('failure');
    }
});

[HttpOptions]
[AllowCrossSiteJson]
[HttpPost]
public ActionResult SendEmail(string email, string name) { //code }

Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: POST
Access-Control-Allow-Headers: Content-Type

public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);
            HttpContext.Current.Response.Cache.SetNoStore();

            filterContext.RequestContext.HttpContext.Response.AppendHeader("Access-Control-Allow-Origin", "*");

            string rqstMethod = HttpContext.Current.Request.Headers["Access-Control-Request-Method"];
            if (rqstMethod == "OPTIONS" || rqstMethod == "POST")
            {
                filterContext.RequestContext.HttpContext.Response.AppendHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
                filterContext.RequestContext.HttpContext.Response.AppendHeader("Access-Control-Allow-Headers", "X-Requested-With, Accept, Access-Control-Allow-Origin, Content-Type");
            }
            base.OnActionExecuting(filterContext);
        }

Allow:OPTIONS, TRACE, GET, HEAD, POST
Connection:keep-alive
Content-Length:0
Date:Wed, 24 Jan 2018 05:04:32 GMT
Public:OPTIONS, TRACE, GET, HEAD, POST
Server:Microsoft-IIS/10.0
X-Powered-By:ASP.NET

Microsoft.AspNet.Cors
Microsoft.Owin.Cors

public partial class Startup
{
    public void Configuration(IAppBuilder app)
    {
        ConfigureAuth(app);

        app.UseCors(CorsOptions.AllowAll);
    }
}