TYPO3 Powermail Validator Class

powermail.ts

plugin.tx_powermail.settings.setup {
    validation {
        customValidation {
            100 = Multivisio\MvMultilindDe\Domain\Validator\PznValidator
        }
    }
}

PznValidator.php

<?php
namespace HenrikZiegenhain\MyExt\Domain\Validator;

/***************************************************************
 *  Copyright notice
 *
 *  (c) 2018 Henrik Ziegenhain <henrik@ziegenhain.me>
 *
 *  All rights reserved
 *
 *  This script is part of the TYPO3 project. The TYPO3 project is
 *  free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  The GNU General Public License can be found at
 *  http://www.gnu.org/copyleft/gpl.html.
 *
 *  This script is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  This copyright notice MUST APPEAR in all copies of the script!
 ***************************************************************/

use TYPO3\CMS\Core\Utility\GeneralUtility;

class PznValidator
{
    /**
     * Check if given string is in list of elements
     *
     * @param string $value
     * @param string $validationConfiguration
     * @return bool
     */
    public function validate100($value, $validationConfiguration)
    {
        if (GeneralUtility::inList($validationConfiguration, $value)) {
            return TRUE;
        }
        return FALSE;
    }
}