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Sandbox Channels are your safe, self-contained space to develop and test email integrations without sending to real inboxes. A Sandbox Channel behaves exactly like a regular Channel - you can send through the API or SMTP, inspect messages, trigger webhooks, and check stats - except the emails never leave Helo.

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When to use a Sandbox Channel

Sandbox Channels are good for:
  • Building your integration - Test your API calls, SMTP setup, and payload formatting without worrying about test emails landing in someone’s inbox.
  • Checking templates - Send real messages through the API and inspect them in the Helo dashboard to confirm they are working correctly.
  • Testing webhooks - Sandbox messages trigger delivery webhooks just like live messages do, so you can build and test your webhook handlers end-to-end.
  • Supporting QA and staging environments - Point your staging app at a Sandbox Channel so your team can test freely without any risk.
Tip: Create API credentials that work with your Sandbox Channel. When setting up new API credentials, you can decide to scope them to a single Channel only, allowing you to further isolate your testing environments.

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How Sandbox Channels work

Sandbox Channels process messages through Helo’s infrastructure the same way live sends do, excluding the final step (delivering to recipient mail servers). That means:
  • Messages show up as Sent in your dashboard and via the API (even though we don’t actually deliver them to real inboxes).
  • All message properties (headers, recipient, subject, body, etc) are stored and inspectable.
  • Webhooks associated with sandbox messages fire normally.
  • Bounce simulation is supported (see simulating bounces)
Heads up: Because Sandbox messages are processed through Helo’s infrastructure, they are billed as part of your monthly sending usage, just like live messages.