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How to Spool Emails

When you are using the SwiftmailerBundle to send an email from a Symfony2 application, it will default to sending the email immediately. You may, however, want to avoid the performance hit of the communication between Swift Mailer and the email transport, which could cause the user to wait for the next page to load while the email is sending. This can be avoided by choosing to "spool" the emails instead of sending them directly. This means that Swift Mailer does not attempt to send the email but instead saves the message to somewhere such as a file. Another process can then read from the spool and take care of sending the emails in the spool. Currently only spooling to file or memory is supported by Swift Mailer.

Spool using memory

When you use spooling to store the emails to memory, they will get sent right before the kernel terminates. This means the email only gets sent if the whole request got executed without any unhandled Exception or any errors. To configure swiftmailer with the memory option, use the following configuration:

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    # app/config/config.yml
    swiftmailer:
        # ...
        spool: { type: memory }
    
  • XML
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    <!-- app/config/config.xml -->
    
    <!--
        xmlns:swiftmailer="http://symfony.com/schema/dic/swiftmailer"
        http://symfony.com/schema/dic/swiftmailer http://symfony.com/schema/dic/swiftmailer/swiftmailer-1.0.xsd
    -->
    
    <swiftmailer:config>
         <swiftmailer:spool type="memory" />
    </swiftmailer:config>
    
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    // app/config/config.php
    $container->loadFromExtension('swiftmailer', array(
         ...,
        'spool' => array('type' => 'memory')
    ));
    

Spool using a file

In order to use the spool with a file, use the following configuration:

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    # app/config/config.yml
    swiftmailer:
        # ...
        spool:
            type: file
            path: /path/to/spool
    
  • XML
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    <!-- app/config/config.xml -->
    
    <!--
        xmlns:swiftmailer="http://symfony.com/schema/dic/swiftmailer"
        http://symfony.com/schema/dic/swiftmailer http://symfony.com/schema/dic/swiftmailer/swiftmailer-1.0.xsd
    -->
    
    <swiftmailer:config>
         <swiftmailer:spool
             type="file"
             path="/path/to/spool" />
    </swiftmailer:config>
    
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    // app/config/config.php
    $container->loadFromExtension('swiftmailer', array(
         // ...
    
        'spool' => array(
            'type' => 'file',
            'path' => '/path/to/spool',
        ),
    ));
    

Tip

If you want to store the spool somewhere with your project directory, remember that you can use the %kernel.root_dir% parameter to reference the project's root:

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path: "%kernel.root_dir%/spool"

Now, when your app sends an email, it will not actually be sent but instead added to the spool. Sending the messages from the spool is done separately. There is a console command to send the messages in the spool:

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$ php app/console swiftmailer:spool:send --env=prod

It has an option to limit the number of messages to be sent:

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$ php app/console swiftmailer:spool:send --message-limit=10 --env=prod

You can also set the time limit in seconds:

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$ php app/console swiftmailer:spool:send --time-limit=10 --env=prod

Of course you will not want to run this manually in reality. Instead, the console command should be triggered by a cron job or scheduled task and run at a regular interval.