You can enable blog subscriptions so subscribers receive all of your published blog posts. You cannot picky choosy which posts they will receive. It's all or nothing. Please see here > http://en.support.wordpress.com/blog-subscriptions/
and here http://en.support.wordpress.com/widgets/blog-subscription-widget/
If you wish you can set up a separate blog for newsletter subscribers. could set up a blog that’s strictly for newsletters and then set up a blog subscription widget on the blog. Every post in the blog would be a newsletter and subscribers get the newsletters by email.
Tip from WordPress.com Support Documentation: Companies may want to create a specific blog to use just for newsletters. If you already own a domain name, you could even get a subdomain such as newsletters.mycompany.com. See the subdomains help page for more details about custom subdomains