我正在尝试设置2个CORS策略。一个作为API默认值，另一个在我需要时在Controllers上使用。我想这样做的原因是因为我有一个端点，它接收一个带有电子邮件信息的对象并发送一封电子邮件（与我网页上的“联系我”框一起使用），并让它只接受来自我的域的请求。
我的startup.cs文件片段：

public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors(options =>
            {
                options.AddPolicy("Example",
                    builder => builder.WithOrigins("http://www.example.com"));
                options.AddPolicy("AllowAll",
                    builder => builder.AllowAnyOrigin());
            });

            services.AddMvc();
            //other configure stuff
        }

 public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        app.UseCors(builder =>
        {
            builder.AllowAnyHeader();
            builder.AllowAnyMethod();
            builder.WithOrigins("AllowAll");
        });

        app.UseMvcWithDefaultRoute();
    }

我的emailcontroller.cs文件：

using System.Threading.Tasks;
using MyAPI.Models;
using MyAPI.Services;
using Microsoft.AspNetCore.Cors;
using Microsoft.AspNetCore.Mvc;

namespace MyAPI.Controllers
{
    [Produces("application/json")]
    [Route("api/Email")]
    [EnableCors("Example")]
    public class EmailController : Controller
    {
        private readonly IEmailSender _emailSender;

        public EmailController(IEmailSender emailSender)
        {
            _emailSender = emailSender;
        }

        [HttpPost]
        public async Task Post([FromBody] Email email)
        {
            await _emailSender.SendEmailAsync(email);
        }
    }

}

用于发送电子邮件的JavaScript：

function sendEmail(email)
{
    var urlToApi = "http://<ipToApi>:5000/api";
    $.ajax({
            method: "POST",
            contentType: "application/json; charset=utf-8",
            data: JSON.stringify(email),     
            url: urlToApi + "/email/",
            success: function(data) {  
                console.log(data);
                console.log('probably sent');
            },
            error: function(jqXHR, textStatus, errorThrown){
                console.log(textStatus);
                alert("There was like, an error doing that");
            }
        });
}

这是我尝试从http://www.example.com发送的结果

XMLHttpRequest cannot load http://<ipToApi>:5000/api/email/. 
Response to preflight request doesn't pass access control check: 
No 'Access-Control-Allow-Origin' header is present on the requested
 resource. Origin 'http://www.example.com' is therefore not allowed access.

编辑

这一方法：

services.AddCors(options =>
            {
                options.AddPolicy("Example",
                    builder => builder.WithOrigins("http://www.example.com")
                                        .AllowAnyHeader()
                                        .AllowAnyMethod());
                options.AddPolicy("AllowAll",
                    builder => builder.AllowAnyOrigin()
                                        .AllowAnyHeader()
                                        .AllowAnyMethod());
            });