native_mailer.xml

<?xml version="1.0" ?>

<srv:container xmlns="http://symfony.com/schema/dic/monolog"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:srv="http://symfony.com/schema/dic/services"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd
                        http://symfony.com/schema/dic/monolog http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <config>
        <handler name="mailer" type="native_mailer" to-email="foo@example.com" from-email="bar@example.com" subject="a subject">
            <headers>
                <foo>bar</foo>
            </headers>
        </handler>
    </config>
</srv:container>