public function getEmailAddressOfContact(ContactInterface $contact, $useFallback = true)
    {
        // take contacts main-email
        $contactMainEmail = $contact->getMainEmail();
        if ($contact && $contactMainEmail) {
            return $contactMainEmail;
        }

        // fallback take contact's main-account main-email
        $account = $contact->getMainAccount();
        if ($useFallback && $account) {
            return $this->getEmailAddressOfAccount($account);
        }

        return null;
    }