Google Gmail API

The Gmail API is a RESTful API that can be used to access Gmail mailboxes and send mail. For most web applications (including mobile apps), the Gmail API is the best choice for authorized access to a user's Gmail data.

The Gmail API gives you flexible, RESTful access to the user's inbox, with a natural interface to Threads, Messages, Labels, Drafts, History, and. Settings. From the modern language of your choice, your app can use the API to add Gmail features like:

• Read messages from Gmail
• Send email messages
• Modify the labels applied to messages and threads
• Search for specific messages and threads
• Create filters to automatically label, forward, or archive messages

All you need to use the Gmail API is the client library for your choice of language and an app that can authenticate as a Gmail user.

Details can be found here.