Sandbox

Sandbox is where you exercise the Mailhub public API before you point an integration at Production. It speaks the same documented contract as Production — the same operations, the same request and response shapes — so the client you build against Sandbox is the client you ship.

Sandbox and Production credentials

Your Mailhub account has two API keys:

Key	Prefix	Use it with
Sandbox API key	mh_test_	the Sandbox API
Production API key	mh_live_	the Production API

Both are viewed in the authenticated Mailhub application under Account → API Keys, and neither is managed through a public operation. See Prepare Your Mailhub Account.

The prefix tells you which key you are holding. That is all it does: it is a label on the credential, not a switch. It does not select an environment for you, and it does not decide how carriers are called. Whether a credential is accepted is answered by the API you send it to.

Exchange the key for an access token exactly as you would in Production — see Authentication and Token Lifecycle. Obtain the Sandbox base URL for your account from Mailhub and configure it the same way you configure MAILHUB_API_BASE_URL for any environment.

What you can test

The Mailhub public API currently contains 12 operations, and Sandbox serves that same public contract. You can work through a complete integration path:

• exchange an API key for a token, refresh it, and revoke it
• create Orders, list them, read one, and update Order status
• request Rates for a Shipment
• buy a Label, download it, and cancel it

The API Reference is the complete schema source for all twelve. The guides carry the workflows — buy a Label, download a Label, and work with Sub-accounts.

API Playground

The API Playground guide covers the browser tool that runs those same twelve operations against your configured Sandbox API, with authentication handled for you. It is a separate surface from the API Reference, which stays read-only. Open the API Playground when you are ready to send requests.

What Sandbox does not guarantee

Sandbox is a place to exercise the contract, not a preview of your Production results.

Validate against Production before go-live

Do not assume Sandbox behavior establishes Production pricing, carrier availability, carrier-provider environment, billing or postage behavior, data retention, quotas, or runtime parity. Confirm anything that carries cost or depends on your account configuration with Mailhub, and validate in Production before launch.

Treat the documented contract as the thing Sandbox and Production share, and treat everything that depends on your account, your carriers, or the deployment as something to re-check on the other side. The Go-Live Checklist is where that re-checking is written down.

Next steps

• API Playground guide — how the browser tool runs the public operations against Sandbox.
• Move to Production — the switch, and what not to carry over with it.
• Authentication and Token Lifecycle — token exchange, refresh, and revoke.
• Production Readiness — reliability boundaries the contract leaves to your application.