The MyNewsletterBuilder PHP SDK by MyNewsletterBuilder wraps the API to access email marketing capabilities that can be used for newsletter features. It is available for download from the main site and it requires PHP 5+ to interact with the code.
Ubivox, email marketing service, has released a number of its features via the Ubivox API. Ubivox allows marketers to create, track, and manage email marketing campaigns directly in a web browser. Because Ubivox is web-based, no additional software becomes necessary to create top notch campaigns. From simple email marketing to tips, to enterprise grade web based software tools, Ubivox aims to be the go to newsletter partner.
The Streak API integrates its client relationship management (CRM) platform into other applications like MailChimps and Wufoo. The API's webpage reveals that it requires an API key and uses HTTP Basic Auth. The request format supports Create, retrieve, update, and delete (CRUD) with response in JSON. The purpose of the API is to manage CRM relationships through your application.