Added copy plugin

Author: geekdevs

README.md

@@ -54,3 +54,22 @@ swiftmailer:
         file:
             transport: file
 ```
+
+## Copy plugin
+
+Copy plugin is useful to BCC all outgoing emails to specific address (e.g. if you want to monitor everything what you send out).
+
+**Connecting to Symfony:**
+
+Define CopyPlugin as service in `services.yml`:
+
+```
+swiftmailer.mailer.plugin.copy:
+    class: Geekdevs\SwiftMailer\Plugins\CopyPlugin
+    arguments:
+      - "[email protected]"
+    tags:
+      - { name: "swiftmailer.primary.plugin" }
+```
+
+Note the tag `swiftmailer.primary.plugin` where "primary" should be the name of your mailer.

src/SwiftMailer/Plugin/CopyPlugin.php

@@ -0,0 +1,53 @@
+<?php
+namespace Geekdevs\SwiftMailer\Plugin;
+
+/**
+ * Class CopyPlugin
+ * @package Geekdevs\SwiftMailer\Transport
+ */
+class CopyPlugin implements \Swift_Events_SendListener
+{
+    /**
+     * @var string
+     */
+    protected $recipient;
+
+    /**
+     * CopyPlugin constructor.
+     * @param string $recipient
+     */
+    public function __construct($recipient)
+    {
+        $this->recipient = $recipient;
+    }
+
+    /**
+     * @param \Swift_Events_SendEvent $evt
+     */
+    public function beforeSendPerformed(\Swift_Events_SendEvent $evt)
+    {
+        /**
+         * @var \Swift_Message $message
+         */
+        $message = $evt->getMessage();
+        $recipient = $this->recipient;
+        $headers = $message->getHeaders();
+
+        if ($headers->has('to')) {
+            $headers->addMailboxHeader('X-Swift-To', $message->getTo());
+        }
+
+        if ($headers->has('cc')) {
+            $headers->addMailboxHeader('X-Swift-Cc', $message->getCc());
+        }
+
+        $message->addBcc($recipient);
+    }
+
+    /**
+     * @param \Swift_Events_SendEvent $evt
+     */
+    public function sendPerformed(\Swift_Events_SendEvent $evt)
+    {
+    }
+}