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Use a local workflow that exercises the real API without exposing secrets or surprising real recipients.

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Environment variables

Store credentials outside source control: 
MAILCHANNELS_API_KEY=xxx
Add .env to .gitignore and commit a .env.example with placeholder values only.

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Test sending

Start with one recipient you control. Use a subject prefix such as [dev] or [staging] so test mail is easy to identify. Before sending a new template, use the dry-run option to render the message without sending it.

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Local webhook testing

During development:
  1. Run your webhook receiver locally.
  2. Expose it through a temporary HTTPS tunnel.
  3. Register the tunnel URL as your webhook endpoint.
  4. Run webhook validation.
  5. Store the raw test event and verify signature validation before adding business logic.

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Avoid common mistakes

  • Do not put API keys in browser JavaScript.
  • Do not commit .env files, webhook signing keys, or private DKIM keys.
  • Do not test with large recipient lists.
  • Do not use production customer addresses for template experiments.
  • Do not assume a successful API response means inbox placement. Use webhooks and mailbox checks.