[Mime] Simplify adding Parts to an Email

Author: fabpot

Normalizer/MimeMessageNormalizer.php

@@ -62,6 +62,7 @@ public function normalize(mixed $object, string $format = null, array $context =
         if ($object instanceof AbstractPart) {
             $ret = $this->normalizer->normalize($object, $format, $context);
             $ret['class'] = $object::class;
+            unset($ret['seekable'], $ret['cid']);
 
             return $ret;
         }