Symfony version(s) affected: 5.2, symfony/mailer (v5.2.6)

Description
In
vendor\symfony\mailer\Transport\NativeTransportFactory.php line 42

$host = ini_get('smtp'); ... requests the php.ini SMTP environment variable, which is uppercase under windows:
SMTP string
https://www.php.net/manual/en/mail.configuration.php#ini.smtp
... and throws exception!

How to reproduce

Possible Solution
check for uppercase SMTP variable name

Additional context