Configure external users phones and tablets in exchange 2013

I have a single Exchange 2013 server that i cannot seem to make external users work by configuring the phones.

using exchange connectivity analyzer i have RPC Ping problems i cannot seem to find a proper answer.

I only have port 443 incoming from the internet to the Exchange 2013.

TheMicrosoftConnectivityAnalyzeris testing ExchangeActiveSync.Attempting the FolderSync command on the ExchangeActiveSync session.ExchangeActiveSync returned an HTTP 500 response (InternalServerError).Diagnostics:
AAA==_S111_Error:ADOperationException1:ActiveDirectory operation failed on VM-DC-002.ourdomain.com.This error isnot retriable.Additional information:Accessis denied.Active directory response:00000005:SecErr: DSID-031521E1, problem 4003(INSUFF_ACCESS_RIGHTS), data 0_Mbx:VM-EXCH13-001.ourdomain.com_Dc:VM-DC-002.IFARHU.GOB.PA_Throttle0_DBL7_DBS1_CmdHC-

Also,

Attempting to ping RPC proxy correo.ourdomain.com.
 	RPC Proxy can't be pinged.
	Additional Details
A Web exception occurred because an HTTP 404 - NotFound response was received from Unknown.
Headers received:
request-id: 1711b40e-d416-4f8f-ada1-876c5e8719e0
X-CasErrorCode: EndpointNotFound
X-FEServer: VM-EXCH13-001
Content-Length: 0
Cache-Control: private
Date: Tue, 24 Dec 2013 06:57:50 GMT
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Elapsed Time: 222 ms.

Suggestions?