{
   "error":{
      "code":"ResourceNotFound",
      "message":"Resource could not be discovered.",
      "innerError":{
         "request-id":"99b44a33-e5cd-4b69-9730-32d72e1f4ebf",
         "date":"2016-12-11T03:51:37"
      }
   }
}

public async Task<ActionResult> ReadMail()
    {
        try
        {
            string signedInUserID = ClaimsPrincipal.Current.FindFirst(ClaimTypes.NameIdentifier).Value;
            ConfidentialClientApplication cca = new ConfidentialClientApplication(clientId, null,
                new ClientCredential(appKey), new MSALSessionCache(signedInUserID, this.HttpContext));
            string[] scopes = { "Mail.Read" };
            AuthenticationResult result = await cca.AcquireTokenSilentAsync(scopes);

            HttpClient hc = new HttpClient();
            hc.DefaultRequestHeaders.Authorization =
                new System.Net.Http.Headers.AuthenticationHeaderValue("bearer", result.Token);
            HttpResponseMessage hrm = await hc.GetAsync("https://graph.microsoft.com/v1.0/me/messages");
            string rez = await hrm.Content.ReadAsStringAsync();
            ViewBag.Message = rez;

            return View();
        }
        catch (MsalSilentTokenAcquisitionException)
        {
            ViewBag.Relogin = "true";
            return View();
        }
        catch (Exception eee)
        {
            ViewBag.Error = "An error has occurred. Details: " + eee.Message;
            return View();
        }
    }