IIRC the email limit is 50MB these days and I'm not a fan of OAuth, it doesnt work in the background since it requires user interaction every time auth is needed. Not to mention that email works with all services, this API with only Kindle.
You can send on news download from a plugin like this:
Code:
self.orig_email_news = self.gui.email_news
self.gui.email_news = self.news_downloaded
def news_downloaded(self, book_id):
... do whatever you want...
self.orig_email_news(book_id)