The unofficial Constant Contact Python SDK by Lambert Wang provides access campaign marketing features of the API with installation and documentation resources. Install with pip and visit the API documentation available at http://developer.constantcontact.com/docs/developer-guides/api-documentation-index.html
As a developer, you can figure out how to make your program connect to Facebook, Twitter, SMS, and Email. Or you can use the Embarke API and connect just to Embarke, a messaging platform that connects you to them all. You can skip learning the specifics of how to connect to each of them. The REST API's website has a five minute tutorial video on how to use this gateway to its developer tools for social communications.
Rebelmail publicly launched its interactive email API. After successful private integrations with ESPs like Mailjet, SendGrid, and others; Rebelmail is ready for third party integrations across the board. Through the API, users can build, send, and track interactive emails directly within an app.
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.