diff --git a/framework/core/src/Extend/Mail.php b/framework/core/src/Extend/Mail.php
new file mode 100644
index 000000000..37058546a
--- /dev/null
+++ b/framework/core/src/Extend/Mail.php
@@ -0,0 +1,38 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Extension\Extension;
+use Illuminate\Contracts\Container\Container;
+
+class Mail implements ExtenderInterface
+{
+    protected $drivers = [];
+
+    /**
+     * Add a mail driver.
+     *
+     * @param string $identifier Identifier for mail driver. E.g. 'smtp' for SmtpDriver
+     * @param string $driver ::class attribute of driver class, which must implement Flarum\Mail\DriverInterface
+     */
+    public function driver(string $identifier, $driver)
+    {
+        $this->drivers[$identifier] = $driver;
+
+        return $this;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        $container->extend('mail.supported_drivers', function ($existingDrivers) {
+            return array_merge($existingDrivers, $this->drivers);
+        });
+    }
+}
diff --git a/framework/core/tests/integration/extenders/MailTest.php b/framework/core/tests/integration/extenders/MailTest.php
new file mode 100644
index 000000000..c18cce91a
--- /dev/null
+++ b/framework/core/tests/integration/extenders/MailTest.php
@@ -0,0 +1,127 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration\extenders;
+
+use Flarum\Extend;
+use Flarum\Mail\DriverInterface;
+use Flarum\Settings\SettingsRepositoryInterface;
+use Flarum\Tests\integration\BuildsHttpRequests;
+use Flarum\Tests\integration\RetrievesAuthorizedUsers;
+use Flarum\Tests\integration\TestCase;
+use Illuminate\Contracts\Validation\Factory;
+use Illuminate\Support\MessageBag;
+use Swift_NullTransport;
+use Swift_Transport;
+
+class MailTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+    use BuildsHttpRequests;
+
+    protected function prepDb()
+    {
+        $this->prepareDatabase([
+            'users' => [
+                $this->adminUser(),
+                $this->normalUser(),
+            ],
+        ]);
+    }
+
+    /**
+     * @test
+     */
+    public function custom_driver_doesnt_exist_by_default()
+    {
+        $this->prepDb();
+
+        $response = $this->send(
+            $this->requestAsUser(
+                $this->request('GET', '/api/mail-settings'),
+                1
+            )
+        );
+
+        $drivers = json_decode($response->getBody(), true)['data']['attributes']['fields'];
+
+        $this->assertArrayNotHasKey('custom', $drivers);
+    }
+
+    /**
+     * @test
+     */
+    public function added_driver_appears_in_mail_settings()
+    {
+        $this->extend(
+            (new Extend\Mail())
+                ->driver('custom', CustomDriver::class)
+        );
+
+        $this->prepDb();
+
+        $response = $this->send(
+            $this->requestAsUser(
+                $this->request('GET', '/api/mail-settings'),
+                1
+            )
+        );
+
+        $drivers = json_decode($response->getBody(), true)['data']['attributes']['fields'];
+
+        $this->assertArrayHasKey('custom', $drivers);
+    }
+
+    /**
+     * @test
+     */
+    public function adding_driver_with_duplicate_name_overrides_fields()
+    {
+        $this->extend(
+            (new Extend\Mail())
+                ->driver('smtp', CustomDriver::class)
+        );
+
+        $this->prepDb();
+
+        $response = $this->send(
+            $this->requestAsUser(
+                $this->request('GET', '/api/mail-settings'),
+                1
+            )
+        );
+
+        $requiredFields = json_decode($response->getBody(), true)['data']['attributes']['fields']['smtp'];
+
+        $this->assertEquals($requiredFields, ['customSetting1' => '']);
+    }
+}
+
+class CustomDriver implements DriverInterface
+{
+    public function availableSettings(): array
+    {
+        return ['customSetting1' => ''];
+    }
+
+    public function validate(SettingsRepositoryInterface $settings, Factory $validator): MessageBag
+    {
+        return new MessageBag;
+    }
+
+    public function canSend(): bool
+    {
+        return false;
+    }
+
+    public function buildTransport(SettingsRepositoryInterface $settings): Swift_Transport
+    {
+        return new Swift_NullTransport();
+    }
+}