Postmark

Authentication

Requests are authenticated with an API key. Keep keys on the server side (for example in a serverless function) and never ship them in front-end code or public repositories.

Pricing model

A free tier is available for getting started, with paid plans for higher limits or commercial features. Confirm whether the free tier allows commercial use. Prices change often, so check the provider's pricing page before you commit, and model your bill at 10× today's volume.

Before you integrate

• Read the terms on caching, storing and displaying data.
• Note the rate limits and the error format so you can retry with backoff.
• Wrap calls behind your own interface so you can switch providers later.
• Pin an API version if the provider offers versioning, and watch its changelog.

Alternatives to Postmark