code: protected function processAttachments(array $attachments)
      {
          $attachments = AttachmentUtils::processAttachments($attachments);
          $processedAttachments = [];
  
          foreach ($attachments as $name => $attachment) {
              $item = [
                  'content'  => base64_encode(file_get_contents($attachment->getPath())),
                  'type'     => $attachment->getType(),
                  'filename' => $attachment->getName(),
              ];
  
              $id = $attachment->getId();
              if (!empty($id)) {
                  $item['disposition'] = 'inline';
                  $item['content_id'] = $id;
              }
  
              $processedAttachments[] = $item;
          }
  
          return $processedAttachments;
      }
docs: @param Attachment[] $attachments
  
  @return array First element: All attachments – array(name => path). Second element: Inline attachments – array(id => name)