We've had a few support requests asking about testing email in our development environment. A test environment is crucial to avoid sending email to real users by mistake and to inspect outbound messages for proper display and headers. Two solutions exist: testing with the API using a "POSTMARK_API_TEST" key, which ensures valid requests but doesn't allow message inspection, or using SMTP with MockSMTP, an open-source app that creates a local server for point-to-point email testing, allowing message content inspection without sending live emails.