Filter systemnotes by field

The post https://usergroup.netsuite.com/users/showthread.php?t=7567 was a helpful start for searching systemnotes. The goal is to retrieve customer email changes. To limit the number of results, a filter on the systemnotes 'date' field works, however filters on 'field' or 'type' return zero results or throw errors about invalid filters. What would be the correct syntax to filter systemnotes by field = 'email' ?

  var filters = new Array();    filters[0] = new nlobjSearchFilter('internalid', null, 'is', '407');    filters[1] = new nlobjSearchFilter('date', 'systemnotes', 'onorafter', 'today'); // Works    filters[2] = new nlobjSearchFilter('field', 'systemnotes', 'is', 'email');   // No results returned.      var columns = new Array();    columns[0] = new nlobjSearchColumn('type', 'systemnotes')    columns[1] = new nlobjSearchColumn('field', 'systemnotes')    columns[2] = new nlobjSearchColumn('date', 'systemnotes')    columns[3] = new nlobjSearchColumn('newvalue', 'systemnotes')    columns[4] = new nlobjSearchColumn('oldvalue', 'systemnotes')      var results = nlapiSearchRecord('customer', null, filters, columns)