issue

js
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var MailBody = document.querySelector('#Mail').innerHTML;
    var MailBody = btoa(MailBody);

    var xhttp = new XMLHttpRequest();
    xhttp.open("POST", "http://localhost:50975/api/maildata",true);
    xhttp.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
    var input = JSON.stringify({
      "MailMessage": MailBody
    });
    xhttp.send(input);

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asp.net controller
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using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using MailAPI.Models;
using Newtonsoft.Json;

namespace MailAPI.Controllers
{
    public class Test : Controller
    {
        [HttpPost("api/maildata")]
        public string SendMail([FromBody]List<MailBody> Mail)
        {
            var json = JsonConvert.SerializeObject(Mail);
            Console.Write("succes");
            return json;
        }
    }
}
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asp.net Model
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using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace MailAPI.Models
{
    public class MailClass
    {
        public string to { get; set; }
        public string subject { get; set; }
        public string body { get; set; }

    }

    public class MailBody
    {
        public string MailMessage { get; set; }
    }
}

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