added support for ENVELOPE fetch

lib/Connection.js

@@ -20,6 +20,7 @@ var MAX_INT = 9007199254740992,
       'RFC822.SIZE': 'size',
       'BODY': 'struct',
       'BODYSTRUCTURE': 'struct',
+      'ENVELOPE': 'envelope',
       'INTERNALDATE': 'date'
     },
     CRLF = '\r\n',
@@ -714,6 +715,8 @@ Connection.prototype._fetch = function(which, uids, options) {
 
   if (options) {
     modifiers = options.modifiers;
+    if (options.envelope)
+      fetching.push('ENVELOPE');
     if (options.struct)
       fetching.push('BODYSTRUCTURE');
     if (options.size)