MAILER configuration with Mandrill?

Hello, I tried to configured Sylius with Mandrill but I can’t achieve to do it.

I checked here:
So I have to configure MAILER_URL on .env file ; OK.

I read that: “In Sylius emails are configured the Symfony way, so you can get inspired by the Symfony guides to those mailing services.”
So, I went to:

But here they talk about MAILER_DSN conf and not MAILER_URL!

I have my Mandrill API KEY but what should I do to connect my Sylius website with my Mandrill account?
Can someone help me on this?

Thanks by advance.