symfony/src/Symfony/Bundle/SwiftmailerBundle/Resources/config/smtp.xml

<?xml version="1.0" encoding="UTF-8" ?>

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

    <parameters>
        <parameter key="swiftmailer.transport.smtp.class">Swift_Transport_EsmtpTransport</parameter>
    </parameters>

    <services>
        <service id="swiftmailer.transport.smtp" class="%swiftmailer.transport.smtp.class%" public="false">
            <argument type="service" id="swiftmailer.transport.buffer" />
            <argument type="collection">
                <argument type="service" id="swiftmailer.transport.authhandler" />
            </argument>
            <argument type="service" id="swiftmailer.transport.eventdispatcher" />

            <call method="setHost"><argument>%swiftmailer.transport.smtp.host%</argument></call>
            <call method="setPort"><argument>%swiftmailer.transport.smtp.port%</argument></call>
            <call method="setEncryption"><argument>%swiftmailer.transport.smtp.encryption%</argument></call>
            <call method="setUsername"><argument>%swiftmailer.transport.smtp.username%</argument></call>
            <call method="setPassword"><argument>%swiftmailer.transport.smtp.password%</argument></call>
            <call method="setAuthMode"><argument>%swiftmailer.transport.smtp.auth_mode%</argument></call>
        </service>
    </services>
</container>