The biggest problem with that is that html and css used in web pages is much different than html and css that works in email. So it is not so easy to take content formatted for web browsers and make it look good in email. Email clients work much differently than web browsers even if they are web based email and there is a lot of differences across different email clients, Outlook, gmail, hotmail, etc etc. So it is very challenging to compose html email that renders consistently and looks good.
Really the goal of a newsletter is to bring visitors back to your site. What I would do is put just links and snippets about your blog posts so that users can click the link in the newsletter and visit your blog to read the full article.
Best,
Joe