Postmark has been reworking its bounce processing and categorization to improve deliverability for its customers. The company tested various methods, including comparing the results of new and old categorization methods, analyzing tens of thousands of bounces with different code libraries, and parsing out valuable information from raw messages using List Nanny and PowerMTA categories. A dynamic approach was needed to handle multiple sources of input, which led to the development of a JSON document that formalizes If-Then statements for recategorizing bounces. This change allows customers to easily add or modify rules, reducing miscategorized Hard Bounces and deactivations, while improving overall deliverability and customer satisfaction.