diff --git a/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd b/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd
index 04157511dc1a..69deb492a2c8 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd
+++ b/src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd
@@ -33,6 +33,7 @@
             <xsd:element name="lock" type="lock" minOccurs="0" maxOccurs="1" />
             <xsd:element name="messenger" type="messenger" minOccurs="0" maxOccurs="1" />
             <xsd:element name="http-client" type="http_client" minOccurs="0" maxOccurs="1" />
+            <xsd:element name="mailer" type="mailer" minOccurs="0" maxOccurs="1" />
         </xsd:choice>
 
         <xsd:attribute name="http-method-override" type="xsd:boolean" />
@@ -543,4 +544,8 @@
     <xsd:complexType name="http_header" mixed="true">
         <xsd:attribute name="name" type="xsd:string" />
     </xsd:complexType>
+
+    <xsd:complexType name="mailer">
+        <xsd:attribute name="dsn" type="xsd:string" />
+    </xsd:complexType>
 </xsd:schema>
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/php/mailer.php b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/php/mailer.php
new file mode 100644
index 000000000000..74f6856c2924
--- /dev/null
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/php/mailer.php
@@ -0,0 +1,7 @@
+<?php
+
+$container->loadFromExtension('framework', [
+    'mailer' => [
+        'dsn' => 'smtp://example.com',
+    ],
+]);
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/xml/mailer.xml b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/xml/mailer.xml
new file mode 100644
index 000000000000..5faa09d36d1b
--- /dev/null
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/xml/mailer.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" ?>
+
+<container xmlns="http://symfony.com/schema/dic/services"
+           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+           xmlns:framework="http://symfony.com/schema/dic/symfony"
+           xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd
+                        http://symfony.com/schema/dic/symfony https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
+
+    <framework:config>
+        <framework:mailer dsn="smtp://example.com" />
+    </framework:config>
+</container>
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/yml/mailer.yml b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/yml/mailer.yml
new file mode 100644
index 000000000000..0fca3e83e054
--- /dev/null
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/yml/mailer.yml
@@ -0,0 +1,3 @@
+framework:
+    mailer:
+        dsn: 'smtp://example.com'
diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
index 877e79c8899e..76e4a086f4d7 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php
@@ -55,7 +55,6 @@
 use Symfony\Component\Validator\DependencyInjection\AddConstraintValidatorsPass;
 use Symfony\Component\Validator\Mapping\Loader\PropertyInfoLoader;
 use Symfony\Component\Validator\Util\LegacyTranslatorProxy;
-use Symfony\Component\Validator\Validation;
 use Symfony\Component\Workflow;
 
 abstract class FrameworkExtensionTest extends TestCase
@@ -1552,6 +1551,14 @@ public function testHttpClientFullDefaultOptions()
         ], $defaultOptions['peer_fingerprint']);
     }
 
+    public function testMailer(): void
+    {
+        $container = $this->createContainerFromFile('mailer');
+
+        $this->assertTrue($container->hasAlias('mailer'));
+        $this->assertTrue($container->hasDefinition('mailer.default_transport'));
+    }
+
     protected function createContainer(array $data = [])
     {
         return new ContainerBuilder(new ParameterBag(array_merge([

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