API Update SwiftMailer from v5 to v6

_config/email.yml

@@ -2,7 +2,7 @@
 Name: emailconfig
 ---
 SilverStripe\Core\Injector\Injector:
-  Swift_Transport: Swift_SendmailTransport
+  Swift_Transport: Swift_MailTransport
   Swift_Mailer:
     constructor:
       - '%$Swift_Transport'

docs/en/02_Developer_Guides/10_Email/index.md

@@ -14,15 +14,20 @@ covers how to create an `Email` instance, customise it with a HTML template, the
 Silverstripe CMS provides an API over the top of the [SwiftMailer](http://swiftmailer.org/) PHP library which comes with an
 extensive list of "transports" for sending mail via different services. 
 
-Out of the box, Silverstripe CMS will use the built-in PHP `mail()` command via the `Swift_MailTransport` class. If you'd
-like to use a more robust transport to send mail you can swap out the transport used by the `Mailer` via config:
+Out of the box, Silverstripe CMS will use the built-in PHP `mail()` command via the `Swift_MailTransport` class.
+
+It's highly recommended you upgrade to a more robust transport to send mail for additional security.
+
+To swap out the transport used by the `Mailer`, create a file `app/_config/email.yml`
+
+To use a `sendmail` binary:
 
 ```yml
 SilverStripe\Core\Injector\Injector:
   Swift_Transport: Swift_SendmailTransport
 ```
 
-For example, to use SMTP, create a file `app/_config/email.yml`:
+To use SMTP:
 
 ```yml
 ---

src/Control/Email/Email.php

@@ -10,6 +10,7 @@
 use SilverStripe\Core\Convert;
 use SilverStripe\Core\Environment;
 use SilverStripe\Core\Injector\Injector;
+use SilverStripe\ORM\FieldType\DBDatetime;
 use SilverStripe\ORM\FieldType\DBField;
 use SilverStripe\ORM\FieldType\DBHTMLText;
 use SilverStripe\View\Requirements;
@@ -272,7 +273,9 @@ public function getSwiftMessage()
      */
     public function setSwiftMessage($swiftMessage)
     {
-        $swiftMessage->setDate(new DateTime());
+        $dateTime = new DateTime();
+        $dateTime->setTimestamp(DBDatetime::now()->getTimestamp());
+        $swiftMessage->setDate($dateTime);
         if (!$swiftMessage->getFrom() && ($defaultFrom = $this->config()->get('admin_email'))) {
             $swiftMessage->setFrom($defaultFrom);
         }
@@ -454,6 +457,9 @@ public function addBCC($address, $name = null)
         return $this;
     }
 
+    /**
+     * @return mixed
+     */
     public function getReplyTo()
     {
         return $this->getSwiftMessage()->getReplyTo();

src/Control/Email/Swift/MailTransport.php

@@ -0,0 +1,77 @@
+<?php
+
+/**
+ * This file was copied in from swiftmailer/swiftmailer v5.4.12 after it was removed from switftmailer v6
+ * It has been slightly modified to meet phpcs standards and initialise Swift_DependencyContainer
+ */
+
+/*
+ * This file is part of SwiftMailer.
+ * (c) 2004-2009 Chris Corbyn
+ *
+ * For the full copyright and license information, please view the LICENSE file (MIT)
+ * https://github.com/swiftmailer/swiftmailer/blob/181b89f18a90f8925ef805f950d47a7190e9b950/LICENSE
+ */
+
+/**
+ * Sends Messages using the mail() function.
+ *
+ * @author Chris Corbyn
+ *
+ * at deprecated since 5.4.5 (to be removed in 6.0)
+ *
+ * @internal
+ */
+// @codingStandardsIgnoreStart
+// ignore missing namespace
+class Swift_MailTransport extends Swift_Transport_MailTransport
+// @codingStandardsIgnoreEnd
+{
+    /**
+     * Create a new MailTransport, optionally specifying $extraParams.
+     *
+     * @param string $extraParams
+     */
+    public function __construct($extraParams = '-f%s')
+    {
+        call_user_func_array(
+            [$this, 'Swift_Transport_MailTransport::__construct'],
+            $this->getDependencies()
+        );
+
+        $this->setExtraParams($extraParams);
+    }
+
+    /**
+     * Create a new MailTransport instance.
+     *
+     * @param string $extraParams To be passed to mail()
+     *
+     * @return self
+     */
+    public static function newInstance($extraParams = '-f%s')
+    {
+        return new self($extraParams);
+    }
+
+    /**
+     * Add in deps for MailTransport which was removed as part of SwiftMailer v6
+     * @see transport_deps.php
+     *
+     * @return array
+     */
+    private function getDependencies(): array
+    {
+        $deps = Swift_DependencyContainer::getInstance()->createDependenciesFor('transport.mail');
+        if (empty($deps)) {
+            Swift_DependencyContainer::getInstance()
+                ->register('transport.mail')
+                ->asNewInstanceOf('Swift_Transport_MailTransport')
+                ->withDependencies(['transport.mailinvoker', 'transport.eventdispatcher'])
+                ->register('transport.mailinvoker')
+                ->asSharedInstanceOf('Swift_Transport_SimpleMailInvoker');
+            $deps = Swift_DependencyContainer::getInstance()->createDependenciesFor('transport.mail');
+        }
+        return $deps;
+    }
+}

src/Control/Email/Swift/Transport/MailInvoker.php

@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * This file was copied in from swiftmailer/swiftmailer v5.4.12 after it was removed from switftmailer v6
+ * It has been slightly modified to meet phpcs standards
+ */
+
+/*
+ * This file is part of SwiftMailer.
+ * (c) 2004-2009 Chris Corbyn
+ *
+ * For the full copyright and license information, please view the LICENSE file (MIT)
+ * https://github.com/swiftmailer/swiftmailer/blob/181b89f18a90f8925ef805f950d47a7190e9b950/LICENSE
+ */
+
+/**
+ * This interface intercepts calls to the mail() function.
+ *
+ * @author     Chris Corbyn
+ *
+ * @internal
+ */
+// @codingStandardsIgnoreStart
+// ignore missing namespace
+interface Swift_Transport_MailInvoker
+// @codingStandardsIgnoreEnd
+{
+    /**
+     * Send mail via the mail() function.
+     *
+     * This method takes the same arguments as PHP mail().
+     *
+     * @param string $to
+     * @param string $subject
+     * @param string $body
+     * @param string $headers
+     * @param string $extraParams
+     *
+     * @return bool
+     */
+    public function mail($to, $subject, $body, $headers = null, $extraParams = null);
+}