Automatic Newsletters Generated From Post

I need help finding a way to automatically generate and send HTML-formatted email newsletters to my subscribers whenever I make a post. In other words, once I make a post on WordPress, I want that same content (which contains media, custom HTML, etc.) to automatically be sent to all of my email subscribers, all within a pre-determined custom HTML email template (that is, the post I made in WordPress is sandwiched between an email header and footer).

Right now, the way I do this is (1) make the post in WP, (2) copy the post content, (3) paste the content into an HTML template document, (4) copy that entire document, (5) paste it into Constant Contact, and (6) initiate the newsletter send from Constant Contact. That’s a very manual process with a lot of steps, and I’m looking to automate this.

Feedburner and RSS won’t cut it. We use Constant Contact for our email list management, but happy to switch to another provider if that gets me what I need.

Does anyone know how to do this?