Yahoo Mail announced a SOAP and JSON–RPC API this morning at Yahoo! Hack Day. The new calls allow any developer to access a Yahoo! user’s existing mail preferences, messages, folders, and change data through create, delete or flag. Documentation of the pre-release API is currently only available through the Yahoo! Mail developer mailing list.
You can do pretty much everything that’s possible with the new Yahoo! Mail beta, including searching mail messages (including attachments), fetching mail from external POP accounts, scrubbed HTML message bodies, and MIME decodings. I’m pretty impressed with the amount of effort spent on these APIs and their release two weeks after availability of public beta.
It’s possible to batch your API requests and responses for efficiency. Data for free Yahoo! Mail users is restricted to mail headers only; premium accounts have full access. The API is only enabled on one mail farm (farm 318) today, but the team expects full deployment in the coming months.