# Test emails safely with Mailtrap Sandbox

Developers need to verify outbound email without sending to real recipients. This skill guides Claude and Codex to configure and use the Mailtrap Email Sandbox for safe, automated email testing in development and CI environments.

## Install

```bash
npx skillstore add mailtrap/testing-with-sandbox
```

## Metadata

- - Slug: mailtrap-testing-with-sandbox
- - Version: 1.0.0
- - Author: mailtrap
- - GitHub username: mailtrap
- - License: MIT
- - Repository: https://github.com/mailtrap/mailtrap-skills/tree/main/skills/testing-with-sandbox
- - Ref: main
- - Supported tools: Claude, Codex, Claude Code
- - Risk level: low
- - Risk factors: external\_commands, network
- - Quality score: 76
- - Public page: https://skillstore.pages.dev/skills/mailtrap-testing-with-sandbox
- - Manifest: https://skillstore.pages.dev/api/skills/mailtrap-testing-with-sandbox/manifest

## Capabilities

- Guide users to configure SMTP or HTTP API to capture outbound email in a sandbox inbox
- Explain how to obtain and use the Mailtrap sandbox API token and inbox ID
- Reference the correct API endpoints for listing sandboxes, messages, and sending test emails
- Direct users to the right Mailtrap SDK repositories for Node.js, Python, PHP, Ruby, Java, .NET, and CLI
- Help distinguish between sandbox \(test\) and transactional \(live\) email endpoints
- Advise on best practices for avoiding production token misuse and common configuration mistakes

## Use Cases

- Set up email testing in a CI pipeline: A backend developer wants automated tests to verify that their application sends correct email content. Use this skill to configure SMTP settings pointing to the Mailtrap sandbox and assert against captured messages.
- Debug email rendering in development: A frontend developer needs to inspect HTML email output during template development. This skill helps them capture emails in a sandbox inbox and review headers, bodies, and spam scores.
- Integrate email testing into staging environment: A DevOps engineer configuring a staging environment wants to ensure no real emails are sent. This skill provides the SMTP host, port, and token scope guidance needed to safely redirect all outbound mail.

## Prompt Templates

### Configure SMTP for sandbox testing

```
I want to configure my application to send all outbound email to a Mailtrap sandbox inbox instead of real recipients. What SMTP host, port, and credentials should I use?
```

### Send a test email via the Sandbox API

```
Show me how to send a test email to my Mailtrap sandbox inbox using the HTTP API. I have my inbox ID and a sandbox API token ready.
```

### Fetch and assert on captured messages

```
I need to write a test that fetches messages from my Mailtrap sandbox inbox and verifies the subject line and HTML body. What API endpoint should I call?
```

### Troubleshoot sandbox vs transactional confusion

```
My emails are going to real recipients instead of the sandbox. I think I am using the wrong endpoint. How do I make sure I am using the Mailtrap testing API and not the live sending API?
```

## Limitations

- Does not provide framework-by-framework setup tutorials; refers to Mailtrap Integration tab
- Cannot execute actual email sending or API calls; provides guidance only
- Does not cover live email sending; use the sending-emails skill for production ESP integration
- Requires users to supply their own Mailtrap account, sandbox token, and inbox ID

## Best Practices

- Always use a dedicated sandbox-scoped token \($MAILTRAP\_SANDBOX\_API\_TOKEN\) for testing, never reuse a live sending token
- Read the SDK README for current sandbox mode options and constructor flags before generating integration code
- Verify that the inbox ID is supplied in all API calls to associate messages with the correct test inbox

## Anti Patterns

- Using the live transactional API token or endpoint in a development or testing environment
- Assuming sandbox email will be delivered to real recipients instead of captured in the test inbox
- Hardcoding the inbox ID or API token in source code instead of using environment variables

## Security Audit

- - Safe to publish: true
- - Audited at: 2026-06-03T15:09:24.855\+00:00
- - Summary: This is a pure documentation skill \(a single SKILL.md\) describing how to use Mailtrap's Email Sandbox for safe email testing. The 61 static findings are all false positives: the 'external\_commands' detections are markdown code-fence backticks \(not Ruby/shell execution\), 'Hardcoded URL' entries are official Mailtrap documentation and API endpoint references, and 'Weak cryptographic algorithm' triggers come from the word 'token' in the context of API authentication. The 'Email sending capability' detections are the core intended function of this skill. No executable code, no prompt injection, and no malicious intent was found.

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