Postmark has launched open tracking webhooks, allowing developers to receive notifications about email opens in real-time. With webhooks enabled, Postmark will push open tracking data to a specified URL each time an open occurs, providing detailed information about the recipient's behavior. Developers can manage their webhooks using the API, and there is also a developer contest with a 150,000 credit reward for unique implementations of webhooks with open tracking. This feature enhances Postmark's functionality and provides more flexibility for developers to integrate with other services.