Is there a way to turn off community forum notifications off by default?

I create a rule on my mail to move directly to a folder

At the bottom of the email you can unsubscride.

@Vincent, that's just to unfollow the post, not to stop receiving all emails from the community forum.

Unfortunately no. It has to be done by individual thread/post.

You're gonna need to make a special folder. I don't think that's a feature yet.
(edit: when you first make your post, you can uncheck the follow post button right under it)

That feature does not exist yet.