diff --git a/src/Symfony/Component/Mime/RawMessage.php b/src/Symfony/Component/Mime/RawMessage.php
index 62f3491ba12e4..484ffb0073f6a 100644
--- a/src/Symfony/Component/Mime/RawMessage.php
+++ b/src/Symfony/Component/Mime/RawMessage.php
@@ -18,7 +18,8 @@
  */
 class RawMessage
 {
-    private iterable|string $message;
+    /** @var iterable|string|resource */
+    private $message;
     private bool $isGeneratorClosed;
 
     public function __construct(iterable|string $message)
@@ -26,12 +27,23 @@ public function __construct(iterable|string $message)
         $this->message = $message;
     }
 
+    public function __destruct()
+    {
+        if (\is_resource($this->message)) {
+            fclose($this->message);
+        }
+    }
+
     public function toString(): string
     {
         if (\is_string($this->message)) {
             return $this->message;
         }
 
+        if (\is_resource($this->message)) {
+            return stream_get_contents($this->message, -1, 0);
+        }
+
         $message = '';
         foreach ($this->message as $chunk) {
             $message .= $chunk;
@@ -53,10 +65,19 @@ public function toIterable(): iterable
             return;
         }
 
+        if (\is_resource($this->message)) {
+            rewind($this->message);
+            while ($line = fgets($this->message)) {
+                yield $line;
+            }
+
+            return;
+        }
+
         if ($this->message instanceof \Generator) {
-            $message = '';
+            $message = fopen('php://temp', 'w+');
             foreach ($this->message as $chunk) {
-                $message .= $chunk;
+                fwrite($message, $chunk);
                 yield $chunk;
             }
             $this->isGeneratorClosed = !$this->message->valid();