symfony: Mailer Transports to SMTP Cannot Establish Secure Connections

Symfony version(s) affected: 5.0.1

Description
When using the Transport out of the box, the Transport is unable to establish a secure connection. This issue looks similar to https://github.com/symfony/symfony/issues/34064

I am using OpenSSL 1.1.1d and PHP 7.4. I’ve reproduced the issue on PHP 7.3 as well.

The exact error message I receive is:

Connection could not be established with host "ssl://smtp.postmarkapp.com:587": stream_socket_client(): SSL operation failed with code 1. OpenSSL Error messages: error:1408F10B:SSL routines:ssl3_get_record:wrong version number

How to reproduce

$transport = new PostmarkSmtpTransport($key);
$mailer = new Mailer($transport);
$mail = (new Email)->to('test@example.com')
->from('test@example.com')
->subject('Test Email')
->html('Test Email');
$mailer->send($mail);