One way of distinguishing between the two would be that user experience is the cognitive interaction with features. If you start with a basic web app, then add a user chat feature and then a group chat feature, ux would be how new and existing users interact with those features and your entire application.

Put another way, user experience encompasses the design aspects and the behavioral aspects of an app, as where features include the different components that make up the overall user experience. Its the interaction with the existing features that compose the ux.