Postmark's monthly newsletter, "Happy Sending," covers industry news, useful tools, and tips for sending great emails. The company also launched a new API call feature in VS Code that makes it simple to interact with REST APIs. Additionally, Postmark is introducing a new retention add-on that allows users to adjust the length of time message content and activity data are stored. The newsletter features interviews with customers who use Postmark for their projects, including Owen Rogers, who operates the .eco top-level domain. Owen shares his experience using Postmark and provides advice on how to implement and manage email effectively. The newsletter also includes educational videos about email authentication standards, such as DKIM, SPF, and DMARC, which are designed to be engaging and easy to understand.