Salut, ia incearca asa: WordPress as CMS: 4 content block plugins with WYSIWYG editors | WP Garage sau Subscriber Content Lock for WordPress - WordPress | CodeCanyon (este cel care vrei tu), Opt-In Content Locker for WordPress Preview - CodeCanyon (si asta este potrivit criteriilor tale)

Sau daca vrei sa mai cauti, uite aici https://www.google.it/?gws_rd=ssl#q=...s%20newsletter , eu nu am prea avut timp sa caut ca am treaba.

Succes!