Adding email spooling cookbook article

cookbook/email/spool.rst

@@ -0,0 +1,76 @@
+How to Spool Email
+==================
+
+When you are using the ``SwiftmailerBundle`` to send emails from a Symfony2
+application it will by default send the email immediately. You may want
+to avoid the performance hit of the communication between ``Swiftmailer``
+and the email transport taking place at the time. This can be avoided by
+choosing to spool the emails instead of sending them directly. This means
+that ``Swiftmailer`` 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 of the email. Currently only spooling to
+file is supported by ``Swiftmailer``.
+
+In order to use the spool you will need to use the following config:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # app/config/config.yml
+        swiftmailer:
+            # ...
+            spool:
+                type: file
+                path: /path/to/spool
+
+    .. code-block:: xml
+
+        <!-- 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>
+
+    .. code-block:: php
+
+        // app/config/config.php
+        $container->loadFromExtension('swiftmailer', array(
+             // ...
+            'spool' => array(
+                'type' => 'file',
+                'path' => '/path/to/spool',
+            )
+        ));
+
+
+Now when your app sends an email it will not actually be sent but 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:
+
+.. code-block:: bash
+
+    php app/console swiftmailer:spool:send
+
+It has an option to limit the number of messages to be sent:
+
+.. code-block:: bash
+
+    php app/console swiftmailer:spool:send --message-limit=10
+
+You can also set the time limit in seconds:
+
+.. code-block:: bash
+
+    php app/console swiftmailer:spool:send --time-limit=10
+
+Of course you will not want to run this manually in actual use, the console
+command should be triggered by a cron job or scheduled task and run at
+a regular interval.