Make an author not able to edit posts

I understand it can sound as weird request. On my online newspaper I have people registered as subscribers that sometimes sends me articles I want to publish. I also would like to assign these articles to the author, so in order to do that I have to elevate their permission to “author”. But I don’t want they can access the backend. Is there a plugin that permits to let an user be an author (I mean selectable by me in the edit post screen), but don’t access to create or edit posts?
Thank you in advance.