Add smtp transport in controller for Pimcore Mail/SwiftMailer


I need to change the SMTP config in Pimcore 6 with differents hosts, because we send with different Mailservers mails out.
I found that i can change the Transport in swift with

$transport = new Swift_SmtpTransport('', 587, 'ssl'); 
$mail = new \Pimcore\Mail($transport); 

but the Class Swift_SmtpTransport is not in the include path.
i add in the TestController.php
use \Swiftmailer\Swiftmailer\Swift_SmtpTransport;

but in not works, they not fount the Class.
the autoloader use the file /var/www/pimcore/vendor/swiftmailer/swiftmailer/lib/swift_required.php

can anyone help me?