diff --git a/Tests/Transport/RoundRobinTransportTest.php b/Tests/Transport/RoundRobinTransportTest.php
index fff75af..08edb24 100644
--- a/Tests/Transport/RoundRobinTransportTest.php
+++ b/Tests/Transport/RoundRobinTransportTest.php
@@ -13,6 +13,7 @@
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Mailer\Exception\TransportException;
+use Symfony\Component\Mailer\Exception\TransportExceptionInterface;
 use Symfony\Component\Mailer\Transport\RoundRobinTransport;
 use Symfony\Component\Mailer\Transport\TransportInterface;
 use Symfony\Component\Mime\RawMessage;
@@ -60,10 +61,21 @@ public function testSendAllDead()
         $t2 = $this->createMock(TransportInterface::class);
         $t2->expects($this->once())->method('send')->will($this->throwException(new TransportException()));
         $t = new RoundRobinTransport([$t1, $t2]);
-        $this->expectException(TransportException::class);
-        $this->expectExceptionMessage('All transports failed.');
-        $t->send(new RawMessage(''));
-        $this->assertTransports($t, 1, [$t1, $t2]);
+        $p = new \ReflectionProperty($t, 'cursor');
+        $p->setAccessible(true);
+        $p->setValue($t, 0);
+
+        try {
+            $t->send(new RawMessage(''));
+        } catch (\Exception $e) {
+            $this->assertInstanceOf(TransportException::class, $e);
+            $this->assertStringContainsString('All transports failed.', $e->getMessage());
+            $this->assertTransports($t, 0, [$t1, $t2]);
+
+            return;
+        }
+
+        $this->fail('The expected exception was not thrown.');
     }
 
     public function testSendOneDead()
@@ -127,6 +139,34 @@ public function testSendOneDeadAndRecoveryWithinRetryPeriod()
         $this->assertTransports($t, 1, []);
     }
 
+    public function testFailureDebugInformation()
+    {
+        $t1 = $this->createMock(TransportInterface::class);
+        $e1 = new TransportException();
+        $e1->appendDebug('Debug message 1');
+        $t1->expects($this->once())->method('send')->will($this->throwException($e1));
+        $t1->expects($this->once())->method('__toString')->willReturn('t1');
+
+        $t2 = $this->createMock(TransportInterface::class);
+        $e2 = new TransportException();
+        $e2->appendDebug('Debug message 2');
+        $t2->expects($this->once())->method('send')->will($this->throwException($e2));
+        $t2->expects($this->once())->method('__toString')->willReturn('t2');
+
+        $t = new RoundRobinTransport([$t1, $t2]);
+
+        try {
+            $t->send(new RawMessage(''));
+        } catch (TransportExceptionInterface $e) {
+            $this->assertStringContainsString('Transport "t1": Debug message 1', $e->getDebug());
+            $this->assertStringContainsString('Transport "t2": Debug message 2', $e->getDebug());
+
+            return;
+        }
+
+        $this->fail('Expected exception was not thrown!');
+    }
+
     private function assertTransports(RoundRobinTransport $transport, int $cursor, array $deadTransports)
     {
         $p = new \ReflectionProperty($transport, 'cursor');
diff --git a/Transport/RoundRobinTransport.php b/Transport/RoundRobinTransport.php
index d12606e..c5587bb 100644
--- a/Transport/RoundRobinTransport.php
+++ b/Transport/RoundRobinTransport.php
@@ -48,15 +48,19 @@ public function __construct(array $transports, int $retryPeriod = 60)
 
     public function send(RawMessage $message, Envelope $envelope = null): ?SentMessage
     {
+        $exception = null;
+
         while ($transport = $this->getNextTransport()) {
             try {
                 return $transport->send($message, $envelope);
             } catch (TransportExceptionInterface $e) {
+                $exception ??= new TransportException('All transports failed.');
+                $exception->appendDebug(sprintf("Transport \"%s\": %s\n", $transport, $e->getDebug()));
                 $this->deadTransports[$transport] = microtime(true);
             }
         }
 
-        throw new TransportException('All transports failed.');
+        throw $exception ?? new TransportException('No transports found.');
     }
 
     public function __toString(): string