CakePHP：传输配置“gmail”丢失

I'm using CakePHP 3.0.15 so I had to use Cake\Network\Email\Email; instead of use Cake\Mailer\Email;. Anyways, I have my EmailTransport in app.php configured like this:

'EmailTransport' => [
    'gmail' => [
        'className' => 'Smtp',
        'host' => 'ssl://smtp.gmail.com',
        'port' => 465,
        'timeout' => 30,
        'username' => 'examplesender@gmail.com',
        'password' => 's2d5f8t9',
        'client' => null,
        'tls' => null,
    ]
],

And have this in my controller:

    $email = new Email();
    $email->transport('gmail')
        ->to('examplereveiver@gmail.com', 'Example Receiver')
        ->from('examplesender@gmail.com', 'Example Sender')
        ->subject('Test Subject')
        ->send('Message!!!!!');

Then it gives me the error:

Transport config "gmail" is missing.

However, when I configure the transport in my controller, just before using it, like this:

    Email::configTransport('gmail', [
        'host' => 'ssl://smtp.gmail.com',
        'port' => 465,
        'username' => 'examplesender@gmail.com',
        'password' => 's2d5f8t9',
        'className' => 'Smtp'
    ]);

It works and sends the email. Still, I'd like to configure the transport in app.php so I would be able to use the same transport config multiple times.

Thanks!!!