Setup

Add bundle to your project:

composer require mailjet/mailjet-bundle

Add Mailjet\MailjetBundle\MailjetBundle to your AppKernel.php:

$bundles = [
    // ...
    new Mailjet\MailjetBundle\MailjetBundle(),
];

Minimal Configuration

In your config.yml:

mailjet:
    api_key:    "%mailjet.api_key%"
    secret_key: "%mailjet.secret_key%"

More configuration