The Gmail API SDK for .NET contains authentication and authorization with Api Keys and OAuth 2. Examples demonstrate a Google Discovery API sample along with web applications, service accounts, and installed applications.
Google has released an updated Gmail API that functionally replaces the Email Settings API. The Gmail API includes a number of new endpoints that enable features previously unavailable through any Google API. Developers have access to filters, auto-replies, send-as aliases, and more.
Facebook has announced the release of Graph API v2.11 and Messenger Platform v2.2. Facebook Graph API v2.11 includes changes to the Pages API and App Links Host. The latest version of the Messenger Platform includes the availability of the Messenger Broadcast API (open beta) and Page Insights API.
Messaging just got a lot more interesting to look at. Words say a lot, but a picture is worth a thousand of them; imagine the levels of communication that could be achieved using both. Doodle Republic is a messaging platform that provides the tools to create messages that include words and images. Basically, people chat by creating their own art and sending it to friends as a Chatoon. The Doodle Republic Chatoon API makes this functionality available to developers who may want to include it in other applications.