cur[1].toLowerCase(); fix

gistfile1.js

// starting around line 1010 in imap.js
} else { // single part
      next = 7;
      part = {
        // the path identifier for this part, useful for fetching specific
        // parts of a message
        partID: (prefix !== '' ? prefix : '1'),

        // required fields as per RFC 3501 -- null or otherwise
        type: cur[0].toLowerCase(),
        //subtype: cur[1].toLowerCase(),
        params: null, id: cur[3], description: cur[4], encoding: cur[5],
        size: cur[6]
      }
      if (cur.length >= 2 && cur[1].toString() === 'String'){
        part.subtype = cur[1].toLowerCase();
      } else {
        part.subtype = null;
      }
      if (Array.isArray(cur[2])) {
        part.params = {};
        for (var i=0,len=cur[2].length; i<len; i+=2)
          part.params[cur[2][i].toLowerCase()] = cur[2][i+1];
      }
      if (part.type === 'message' && part.subtype === 'rfc822') {
        // envelope