Yahoo announced at Yahoo Hack Day that they'll open Yahoo Mail, so programmers can develop extensions and new interfaces for Yahoo Mail. The new API, that will be available later this year, will use Yahoo's browser-based authentication. Google has a similar API for Google Accounts.
"Chad Dickerson, head of the Sunnyvale company's software developer relations program, said he believed that the open approach to programming represented the biggest single Web software ever to be opened up for public development." Yahoo Mail has more than 257 million users, some of them being spam bots.
Yahoo doesn't include POP3 access for their free mail service, so this API might allow developers to deliver this feature (there are applications that create POP3 servers for Yahoo Mail, but the API will make things easier).
It will be interesting to see if Google follows the trend and provides an official API for Gmail.
Wileyfox Spark hands-on: For $120, this phone is astounding
47 minutes ago