diff --git a/src/Symfony/Component/Mailer/Bridge/Mailchimp/Transport/MandrillApiTransport.php b/src/Symfony/Component/Mailer/Bridge/Mailchimp/Transport/MandrillApiTransport.php
index 068da4d7eb7a0..469354d67bbe7 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailchimp/Transport/MandrillApiTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailchimp/Transport/MandrillApiTransport.php
@@ -121,7 +121,7 @@ private function getPayload(Email $email, Envelope $envelope): array
                 continue;
             }
 
-            $payload['message']['headers'][$name] = $header->getBodyAsString();
+            $payload['message']['headers'][$header->getName()] = $header->getBodyAsString();
         }
 
         return $payload;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Transport/MailgunApiTransportTest.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Transport/MailgunApiTransportTest.php
index 2e4c53b83fc98..5f5b8f32362a1 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Transport/MailgunApiTransportTest.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Transport/MailgunApiTransportTest.php
@@ -65,8 +65,8 @@ public function testCustomHeader()
         $method->setAccessible(true);
         $payload = $method->invoke($transport, $email, $envelope);
 
-        $this->assertArrayHasKey('h:x-mailgun-variables', $payload);
-        $this->assertEquals($json, $payload['h:x-mailgun-variables']);
+        $this->assertArrayHasKey('h:X-Mailgun-Variables', $payload);
+        $this->assertEquals($json, $payload['h:X-Mailgun-Variables']);
     }
 
     public function testSend()
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Transport/MailgunApiTransport.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Transport/MailgunApiTransport.php
index 329b6eeaef449..4607a07037d16 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Transport/MailgunApiTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Transport/MailgunApiTransport.php
@@ -120,7 +120,7 @@ private function getPayload(Email $email, Envelope $envelope): array
                 continue;
             }
 
-            $payload['h:'.$name] = $header->getBodyAsString();
+            $payload['h:'.$header->getName()] = $header->getBodyAsString();
         }
 
         return $payload;
diff --git a/src/Symfony/Component/Mailer/Bridge/Postmark/Transport/PostmarkApiTransport.php b/src/Symfony/Component/Mailer/Bridge/Postmark/Transport/PostmarkApiTransport.php
index 4ccf8762b7a85..e1b4cd3dda8d4 100644
--- a/src/Symfony/Component/Mailer/Bridge/Postmark/Transport/PostmarkApiTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Postmark/Transport/PostmarkApiTransport.php
@@ -93,7 +93,7 @@ private function getPayload(Email $email, Envelope $envelope): array
             }
 
             $payload['Headers'][] = [
-                'Name' => $name,
+                'Name' => $header->getName(),
                 'Value' => $header->getBodyAsString(),
             ];
         }
diff --git a/src/Symfony/Component/Mailer/Bridge/Sendgrid/Transport/SendgridApiTransport.php b/src/Symfony/Component/Mailer/Bridge/Sendgrid/Transport/SendgridApiTransport.php
index 07108f19aab3c..d198be82d7b35 100644
--- a/src/Symfony/Component/Mailer/Bridge/Sendgrid/Transport/SendgridApiTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Sendgrid/Transport/SendgridApiTransport.php
@@ -121,7 +121,7 @@ private function getPayload(Email $email, Envelope $envelope): array
                 continue;
             }
 
-            $payload['headers'][$name] = $header->getBodyAsString();
+            $payload['headers'][$header->getName()] = $header->getBodyAsString();
         }
 
         return $payload;