Symfony version(s) affected: 4.3.8

Description

There is no way to configure the mailer component without a bus. If I have the messenger component in my app mailer automatically works via bus. But I want to send a message instantly without using a message bus
https://github.com/symfony/mailer/blob/4.3/Mailer.php#L29

Possible Solution
Maybe it is a good idea to add the ability to configure this?