Does anyone know a plugin that turns a ‘post’ into an html newsletter?

I know you could just grab the code or some such. But I’m trying to figure out a way to easily implement this for a client.

All my googling has just turned up signup forms, not anything for actually sending out a post.

To summarise what I’m after:

I want the client to be able to create a post, use the built in text editor for formatting etc, maybe attach a picture and so on. So that they can have the complete newsletter archive online.

Then I want a way for them to be able to send it out. Either by exporting the html code (via a template), or linking it direct to mailchimp or some such.

Has anyone had to do something similar? Or do you have any idea of a plugin I should be checking out? If it’s not out there I’m not against trying to write a plugin for this (though I’m not sure how I’d start that yet)… but thought it best to check first.

Thanks