How can anonymous users be allowed to post while still maintaining content integrity?
I don't think this is possible with rules alone.

You need to alter the submission form in order to capture the verification email address, and you also need some logic to ban spammers and recognise returning visitors.

I am the maintainer of a project named Anonymous Publishing. It looks as if this module does what you want.

It still in development, but a Drupal 7 version has been used at several of my production sites without any issues. Please check it out.

You may also want to look at the answers under this question.