private function moveAttachments(Message $from, Swift_Message $to): array
    {
        foreach ($from->content()->attachments() as $path) {
            $to->attach(Swift_Attachment::fromPath($path));
        }
        $cids = [];
        foreach ($from->content()->embeddedAttachments() as $id => $path) {
            $cids[$id] = $to->embed(Swift_Attachment::fromPath($path));
        }

        return $cids;
    }