[hacker256]

Unlisted posting is complete. If you send to [e-mail] (or [e-mail]) the post will not show up in new/popular/categories. However, it will still show up in your user view.

If you want it to be visible with a link only and not even show on your user page, you can send to [e-mail].

Anonymous posting is coming next!

[gitgud]

You could implement email like Craigslist do with an "email relay".

That way the users email is hidden with an anonymous alias. But people can still reply to that alias email.

[hacker256]

This is a great idea. I've actually started down this path a bit, and will add the actual email relay tomorrow!