You can certainly do this directly in Ghost using custom collections. In this example in our docs a new custom collection is being made that puts all members only newsletters into it’s own collection, leaving the blog home page with only public posts:
If you want all your posts to be public you could use a tag instead like so:
In the above example the routes file is taking any post tagged with “newsletter” and placing them in a “/newsletter/” sub page of the site. Again this will leave your main blog free of your emailed posts.
Hope this helps!