code: function redisCheckAccount(options, callback) {
      _debug('le-store-redis.redisCheckAccount:',
        options.email, options.accountId, options.domains);
  
      if(options.email) {
        return _getByIndex('idx-e2a', options.email, callback);
      } else if(options.accountId) {
        return client.get(options.accountId, _deserializeJson(callback));
      } else if(options.domains) {
        // FIXME: implement domain indexing
        return client.get(options.domains, _deserializeJson(callback));
      }
  
      callback(new Error('le-store-redis.redisCheckAccount requires ' +
        'options.email, options.accountId, or options.domains'));
    }
docs: Checks to see if an account exists in the database. The provided options
  describe how the account should be looked up.
  
  @param {Object[]} options - options passed to storage called
  @param {string} options[].email - optional email address to use when
  looking up the account.
  @param {string} options[].accountId - optional accountId to use when
  looking up the account.
  @param {string} options[].domains - optional domains to use when looking
  up the account.
  @param {Function} callback(err, account) - called when an error occurs, or
  when an account is successfully retrieved from the database.