It’s easy to get your Direct Mail API account:
Development - Create a sandbox Postalytics account at app-staging.postalytics.com. When testing against the sandbox, be sure to point your endpoint to https://api-dev.postalytics.com
Production - Create a live Postalytics account (or login to your existing account) at app.postalytics.com. When testing against live, be sure to point your endpoint to https://api.postalytics.com
Get your API key from the Connect section of your Postalytics account