This is what WES says in its documentation about sending your documents to them:
Before you send documents, you must submit an application and get a reference number. Include your WES reference number on all envelopes and correspondence. WES is not responsible for documents that arrive without a reference number. Documents that arrive in our office without a reference number may encounter processing delays.
Do not send original documents unless specifically requested by WES. All documentation received becomes the property of WES and cannot be returned.