Convert to using graceful-fs vs vanilla fs module

core/ftn_mail_packet.js

@@ -11,7 +11,7 @@ const Log			= require('./logger.js').log;
 const _				= require('lodash');
 const assert		= require('assert');
 const binary		= require('binary');
-const fs			= require('fs');
+const fs			= require('graceful-fs');
 const async			= require('async');
 const iconv			= require('iconv-lite');
 const moment		= require('moment');