Not sure what you mean by “mixed up in one post”. If you upload a file to a post, it is not actually stored in that post but somewhere on your server (or on Amazon S3, if you set up the forum like that). What is stored in your post is only the URL of the file on wherever it is stored.
That URL can be used over and over again in many posts, without having to re-upload the original file.
But if your point is that you want to also have those files neatly stored somewhere in a single folder, then it’s probably better to use a cloud storage provider of your choice, upload the files there, make them publicly available via URL and paste that URL in your forum post.