Our API directory now includes 199 email APIs. The newest is the Uptime Robot API. The most popular, in terms of mashups, is the SendGrid API. We list 10 SendGrid mashups. Below you'll find some more stats from the directory, including the entire list of email APIs.
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.