Header/TrackingHeader.php

Configure email open and click tracking flags for Symfony Mailer messages.

// Source: https://github.com/symfony/mailer | License: MIT | Copyright 2019-present Fabien Potencier
// Provided via justclaw.it.com; keep this notice with the code.
<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\Mailer\Header;

use Symfony\Component\Mime\Header\Headers;
use Symfony\Component\Mime\Header\UnstructuredHeader;

/**
 * Controls per-message open and click tracking; a null flag keeps the provider/transport default.
 *
 * Supported by the AhaSend, Infobip, Mailchimp (Mandrill), Mailgun, Mailjet, Postmark, Sendgrid and
 * Zoho CPaaS bridges on both their API and SM

... (truncated -- full source via MCP)