Along with this post about Browser-Based Authentication
http://blogoscoped.com/forum/69765.html

Yahoo has announced that their releasing the Yahoo Mail API with BBAuth.

via Reuters:
Yahoo to give away e-mail code
http://news.com.com/2100-1032_3-6121552.html

From the article:
"Officials of the world's largest Internet media company said on Friday it planned to give away the underlying code to Yahoo Mail, one of the crown jewels of its business, in a bid to encourage software developers to build new applications based on e-mail.

The move to open up the underlying code of Yahoo Mail--used by 257 million people--is designed to spark development of thousands of new e-mail applications built not only by Yahoo engineers but by outside companies and individuals.
<SNIP>
Yahoo Mail's code will be generally available later in 2006 said Jason Rupp, product manager for Yahoo's e-mail services."

Zawodny briefly mentions it in this post.
http://jeremy.zawodny.com/blog/archives/007557.html

Nice find. I'm sorry but How can it be used by developers ?

I guess this would make it possible to write an email application that showed your incoming emails threaded together with your incoming RSS feeds?