diff --git a/.travis.yml b/.travis.yml
index c8f35b41b2..ab6c2d09b8 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -185,7 +185,7 @@ install:
     - |
       # Install the phpunit-bridge from a PR if required
       #
-      # To run a PR with a patched phpunit-bridge, first submit the path for the
+      # To run a PR with a patched phpunit-bridge, first submit the patch for the
       # phpunit-bridge as a separate PR against the next feature-branch then
       # uncomment and update the following line with that PR number
       #SYMFONY_PHPUNIT_BRIDGE_PR=32886
diff --git a/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillAssertTrait.php b/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillAssertTrait.php
index 5d564774a7..69a01d2927 100644
--- a/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillAssertTrait.php
+++ b/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillAssertTrait.php
@@ -17,7 +17,7 @@ use PHPUnit\Framework\Constraint\StringContains;
 use PHPUnit\Framework\Constraint\TraversableContains;
 
 /**
- * This trait is @internal
+ * This trait is @internal.
  */
 trait PolyfillAssertTrait
 {
@@ -251,4 +251,196 @@ trait PolyfillAssertTrait
         static::assertInternalType('float', $actual, $message);
         static::assertTrue(is_nan($actual), $message ? $message : "Failed asserting that $actual is nan.");
     }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertIsReadable($filename, $message = '')
+    {
+        static::assertInternalType('string', $filename, $message);
+        static::assertTrue(is_readable($filename), $message ? $message : "Failed asserting that $filename is readable.");
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertNotIsReadable($filename, $message = '')
+    {
+        static::assertInternalType('string', $filename, $message);
+        static::assertFalse(is_readable($filename), $message ? $message : "Failed asserting that $filename is not readable.");
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertIsWritable($filename, $message = '')
+    {
+        static::assertInternalType('string', $filename, $message);
+        static::assertTrue(is_writable($filename), $message ? $message : "Failed asserting that $filename is writable.");
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertNotIsWritable($filename, $message = '')
+    {
+        static::assertInternalType('string', $filename, $message);
+        static::assertFalse(is_writable($filename), $message ? $message : "Failed asserting that $filename is not writable.");
+    }
+
+    /**
+     * @param string $directory
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertDirectoryExists($directory, $message = '')
+    {
+        static::assertInternalType('string', $directory, $message);
+        static::assertTrue(is_dir($directory), $message ? $message : "Failed asserting that $directory exists.");
+    }
+
+    /**
+     * @param string $directory
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertDirectoryNotExists($directory, $message = '')
+    {
+        static::assertInternalType('string', $directory, $message);
+        static::assertFalse(is_dir($directory), $message ? $message : "Failed asserting that $directory does not exist.");
+    }
+
+    /**
+     * @param string $directory
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertDirectoryIsReadable($directory, $message = '')
+    {
+        static::assertDirectoryExists($directory, $message);
+        static::assertIsReadable($directory, $message);
+    }
+
+    /**
+     * @param string $directory
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertDirectoryNotIsReadable($directory, $message = '')
+    {
+        static::assertDirectoryExists($directory, $message);
+        static::assertNotIsReadable($directory, $message);
+    }
+
+    /**
+     * @param string $directory
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertDirectoryIsWritable($directory, $message = '')
+    {
+        static::assertDirectoryExists($directory, $message);
+        static::assertIsWritable($directory, $message);
+    }
+
+    /**
+     * @param string $directory
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertDirectoryNotIsWritable($directory, $message = '')
+    {
+        static::assertDirectoryExists($directory, $message);
+        static::assertNotIsWritable($directory, $message);
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertFileExists($filename, $message = '')
+    {
+        static::assertInternalType('string', $filename, $message);
+        static::assertTrue(file_exists($filename), $message ? $message : "Failed asserting that $filename exists.");
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertFileNotExists($filename, $message = '')
+    {
+        static::assertInternalType('string', $filename, $message);
+        static::assertFalse(file_exists($filename), $message ? $message : "Failed asserting that $filename does not exist.");
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertFileIsReadable($filename, $message = '')
+    {
+        static::assertFileExists($filename, $message);
+        static::assertIsReadable($filename, $message);
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertFileNotIsReadable($filename, $message = '')
+    {
+        static::assertFileExists($filename, $message);
+        static::assertNotIsReadable($filename, $message);
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertFileIsWritable($filename, $message = '')
+    {
+        static::assertFileExists($filename, $message);
+        static::assertIsWritable($filename, $message);
+    }
+
+    /**
+     * @param string $filename
+     * @param string $message
+     *
+     * @return void
+     */
+    public static function assertFileNotIsWritable($filename, $message = '')
+    {
+        static::assertFileExists($filename, $message);
+        static::assertNotIsWritable($filename, $message);
+    }
 }
diff --git a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
index 19721fb871..196d7d6c7e 100644
--- a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
+++ b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
@@ -528,6 +528,10 @@ class FrameworkExtension extends Extension
             $loader->load('messenger_debug.xml');
         }
 
+        if (class_exists(Mailer::class)) {
+            $loader->load('mailer_debug.xml');
+        }
+
         $container->setParameter('profiler_listener.only_exceptions', $config['only_exceptions']);
         $container->setParameter('profiler_listener.only_master_requests', $config['only_master_requests']);
 
diff --git a/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer_debug.xml b/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer_debug.xml
new file mode 100644
index 0000000000..17ed496661
--- /dev/null
+++ b/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer_debug.xml
@@ -0,0 +1,12 @@
+<?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">
+
+    <services>
+        <service id="mailer.logger_message_listener" class="Symfony\Component\Mailer\EventListener\MessageLoggerListener">
+            <tag name="kernel.event_subscriber"/>
+        </service>
+    </services>
+</container>
diff --git a/src/Symfony/Component/Mailer/CHANGELOG.md b/src/Symfony/Component/Mailer/CHANGELOG.md
index 6a0669faca..76b895a680 100644
--- a/src/Symfony/Component/Mailer/CHANGELOG.md
+++ b/src/Symfony/Component/Mailer/CHANGELOG.md
@@ -4,6 +4,7 @@ CHANGELOG
 4.4.0
 -----
 
+ * Added `MessageEvents` and `MessageLoggerListener` to allow collecting sent emails
  * [BC BREAK] `TransportInterface` has a new `getName()` method
  * [BC BREAK] Classes `AbstractApiTransport` and `AbstractHttpTransport` moved under `Transport` sub-namespace.
  * [BC BREAK] Transports depend on `Symfony\Contracts\EventDispatcher\EventDispatcherInterface`
diff --git a/src/Symfony/Component/Mailer/Event/MessageEvent.php b/src/Symfony/Component/Mailer/Event/MessageEvent.php
index 41c31d442a..84be56d999 100644
--- a/src/Symfony/Component/Mailer/Event/MessageEvent.php
+++ b/src/Symfony/Component/Mailer/Event/MessageEvent.php
@@ -16,7 +16,7 @@ use Symfony\Component\Mime\RawMessage;
 use Symfony\Contracts\EventDispatcher\Event;
 
 /**
- * Allows the transformation of a Message.
+ * Allows the transformation of a Message and the SMTP Envelope before the email is sent.
  *
  * @author Fabien Potencier <fabien@symfony.com>
  */
@@ -24,11 +24,15 @@ class MessageEvent extends Event
 {
     private $message;
     private $envelope;
+    private $transportName;
+    private $queued;
 
-    public function __construct(RawMessage $message, SmtpEnvelope $envelope)
+    public function __construct(RawMessage $message, SmtpEnvelope $envelope, string $transportName, bool $queued = false)
     {
         $this->message = $message;
         $this->envelope = $envelope;
+        $this->transportName = $transportName;
+        $this->queued = $queued;
     }
 
     public function getMessage(): RawMessage
@@ -50,4 +54,14 @@ class MessageEvent extends Event
     {
         $this->envelope = $envelope;
     }
+
+    public function getTransportName(): string
+    {
+        return $this->transportName;
+    }
+
+    public function isQueued(): bool
+    {
+        return $this->queued;
+    }
 }
diff --git a/src/Symfony/Component/Mailer/Event/MessageEvents.php b/src/Symfony/Component/Mailer/Event/MessageEvents.php
new file mode 100644
index 0000000000..a921022ced
--- /dev/null
+++ b/src/Symfony/Component/Mailer/Event/MessageEvents.php
@@ -0,0 +1,51 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mailer\Event;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class MessageEvents
+{
+    private $events = [];
+    private $transports = [];
+
+    public function add(MessageEvent $event): void
+    {
+        $this->events[] = $event;
+        $this->transports[$event->getTransportName()] = true;
+    }
+
+    public function getTransports(): array
+    {
+        return array_keys($this->transports);
+    }
+
+    /**
+     * @return MessageEvent[]
+     */
+    public function getEvents(string $name = null): array
+    {
+        if (null === $name) {
+            return $this->events;
+        }
+
+        $events = [];
+        foreach ($this->events as $event) {
+            if ($name === $event->getTransportName()) {
+                $events[] = $event;
+            }
+        }
+
+        return $events;
+    }
+}
diff --git a/src/Symfony/Component/Mailer/EventListener/MessageLoggerListener.php b/src/Symfony/Component/Mailer/EventListener/MessageLoggerListener.php
new file mode 100644
index 0000000000..093bf2bb9e
--- /dev/null
+++ b/src/Symfony/Component/Mailer/EventListener/MessageLoggerListener.php
@@ -0,0 +1,57 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mailer\EventListener;
+
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\Mailer\Event\MessageEvent;
+use Symfony\Component\Mailer\Event\MessageEvents;
+use Symfony\Contracts\Service\ResetInterface;
+
+/**
+ * Logs Messages.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class MessageLoggerListener implements EventSubscriberInterface, ResetInterface
+{
+    private $events;
+
+    public function __construct()
+    {
+        $this->events = new MessageEvents();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function reset()
+    {
+        $this->events = new MessageEvents();
+    }
+
+    public function onMessage(MessageEvent $event): void
+    {
+        $this->events->add($event);
+    }
+
+    public function getEvents(): MessageEvents
+    {
+        return $this->events;
+    }
+
+    public static function getSubscribedEvents()
+    {
+        return [
+            MessageEvent::class => ['onMessage', -255],
+        ];
+    }
+}
diff --git a/src/Symfony/Component/Mailer/Mailer.php b/src/Symfony/Component/Mailer/Mailer.php
index 324f50cad7..db87602022 100644
--- a/src/Symfony/Component/Mailer/Mailer.php
+++ b/src/Symfony/Component/Mailer/Mailer.php
@@ -11,6 +11,8 @@
 
 namespace Symfony\Component\Mailer;
 
+use Symfony\Component\Mailer\Event\MessageEvent;
+use Symfony\Component\Mailer\Exception\TransportException;
 use Symfony\Component\Mailer\Messenger\SendEmailMessage;
 use Symfony\Component\Mailer\Transport\TransportInterface;
 use Symfony\Component\Messenger\MessageBusInterface;
@@ -38,6 +40,19 @@ class Mailer implements MailerInterface
             return;
         }
 
+        $message = clone $message;
+        if (null !== $envelope) {
+            $envelope = clone $envelope;
+        } else {
+            try {
+                $envelope = new DelayedSmtpEnvelope($message);
+            } catch (\Exception $e) {
+                throw new TransportException('Cannot send message without a valid envelope.', 0, $e);
+            }
+        }
+        $event = new MessageEvent($message, $envelope, $this->transport->getName());
+        $this->dispatcher->dispatch($event);
+
         $this->bus->dispatch(new SendEmailMessage($message, $envelope));
     }
 }
diff --git a/src/Symfony/Component/Mailer/Transport/AbstractTransport.php b/src/Symfony/Component/Mailer/Transport/AbstractTransport.php
index 3dd59c195c..90b04c19ab 100644
--- a/src/Symfony/Component/Mailer/Transport/AbstractTransport.php
+++ b/src/Symfony/Component/Mailer/Transport/AbstractTransport.php
@@ -69,7 +69,7 @@ abstract class AbstractTransport implements TransportInterface
             }
         }
 
-        $event = new MessageEvent($message, $envelope);
+        $event = new MessageEvent($message, $envelope, $this->getName(), true);
         $this->dispatcher->dispatch($event);
         $envelope = $event->getEnvelope();
         if (!$envelope->getRecipients()) {
diff --git a/src/Symfony/Component/Mailer/composer.json b/src/Symfony/Component/Mailer/composer.json
index f9790c2f8a..896f6380c1 100644
--- a/src/Symfony/Component/Mailer/composer.json
+++ b/src/Symfony/Component/Mailer/composer.json
@@ -20,7 +20,8 @@
         "egulias/email-validator": "^2.0",
         "psr/log": "~1.0",
         "symfony/event-dispatcher": "^4.4|^5.0",
-        "symfony/mime": "^4.4|^5.0"
+        "symfony/mime": "^4.4|^5.0",
+        "symfony/service-contracts": "^1.1"
     },
     "require-dev": {
         "symfony/amazon-mailer": "^4.4|^5.0",