code: function emailCheck(email, key) {
    email = email.toLowerCase();
    // escape email before using in regular expression
    const emailEsc = email.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
    const emailRegex = new RegExp('<' + emailEsc + '>');
    const userIds = key.getUserIds();
    for (let i = 0; i < userIds.length; i++) {
      const userId = userIds[i].toLowerCase();
      if (email === userId || emailRegex.test(userId)) {
        return true;
      }
    }
    return false;
  }
docs: Checks a key to see if it matches the specified email address
  @private
  @param {String} email email address to search for
  @param {module:key.Key} key The key to be checked.
  @returns {Boolean} True if the email address is defined in the specified key