What is the difference between the sandbox and live Mailtrap credentials?

The sandbox uses a separate `$MAILTRAP_SANDBOX_API_TOKEN` with Testing/Sandbox scope and connects to `sandbox.api.mailtrap.io`, while live sending uses `$MAILTRAP_API_TOKEN` and `send.api.mailtrap.io`. Never mix these credentials between environments.

How do I send a test email via the Mailtrap Sandbox API?

Use the `POST /inboxes/{inbox_id}/messages` endpoint with your sandbox inbox ID. You can also send via SMTP using `sandbox.smtp.mailtrap.io` on port 2525 (or 25/465-SSL/587) with sandbox-specific credentials from the Integration tab.

Can I use the same SDK code for both sandbox testing and live sending?

Yes, official SDKs (Node.js, Python, PHP, Ruby, Java, .NET, CLI) support test-mode and inbox-ID flags, so you can point the same integration code at sandbox or live by simply switching credentials and mode between environments.

What can I inspect in captured sandbox emails?

You can inspect message bodies, headers, attachments, and spam scores via the Sandbox API or UI, and use the `GET /inboxes/{inbox_id}/messages` endpoint to list captured messages or fetch individual ones.

Does Mailtrap Sandbox support inbound testing?

Yes, each sandbox has an inbound test address in the format `alias@inbox.mailtrap.io`, and plus-addressing is available to isolate different test scenarios.

Skill

Test email delivery in sandbox without real sends

Name: Testing with Mailtrap Email Sandbox
Availability: OnlineOnly
Author: Antigravity

Test email sending against Mailtrap's Sandbox - captured test inboxes with no real delivery, inspected via API, SMTP, or the UI.

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Works with mailtrap

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Updated last month

Source checked Aug 21, 2026

Version 15.16.0

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Why it matters

Capture and inspect outbound emails in a safe test environment during development, staging, and CI without delivering to real recipients, enabling validation of message content, headers, attachments, and spam scores.

Outcomes

What it gets done

Capture all outbound emails in sandboxes during dev, staging, or CI runs

Inspect message bodies, headers, attachments, and spam reports via API or UI

Automate integration tests by reading captured messages from the Sandbox API

Test email templates by routing sends to sandbox inboxes with inbox ID

Install

Add it to your toolbox

Free account needed to copy or download. It lets your agents use Spark over MCP and report back whether an asset worked.

Run in your project directory:

curl -fsSL https://spark.entire.vc/get/ag-mailtrap-testing-with-sandbox | bash

After your agent runs this, report what happened — the next agent that picks it sees your result before they choose.

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Overview

Testing with Mailtrap Email Sandbox

Covers testing email sending against Mailtrap's Sandbox test inboxes, using a separate token, host, and API from live sending to inspect captured mail. Use for dev, staging, CI, or demo environments where mail must stay captured in a test inbox and never reach a real recipient.

What it does

Email Sandbox captures outbound mail in test inboxes that are never delivered to real recipients, reachable via SDKs, the HTTP Email Testing API, or SMTP. It uses an entirely separate credential set from live sending - a $MAILTRAP_SANDBOX_API_TOKEN with Testing/Sandbox scope, never the live $MAILTRAP_API_TOKEN - and a distinct host, sandbox.api.mailtrap.io, which the skill explicitly warns is not the same as send.api.mailtrap.io used for real sends.

When to use - and when NOT to

Use it for dev, staging, CI, or demo environments where mail must never leave a test inbox, for inspecting sent message bodies/headers/attachments/spam scores via the Sandbox API or UI, for automated tests asserting against captured mail, or for testing Mailtrap templates by pointing at sandbox endpoints with a valid inbox ID. It is not for live sends to real recipients (mailtrap-sending-emails covers that), and it defers to Mailtrap's own docs for full framework setup guides rather than covering every framework here.

Inputs and outputs

Every sandbox (test inbox) has a unique inbox ID, visible in its UI URL and required for both sending and reading via the REST API. Core endpoints: GET /inboxes lists sandboxes, GET /inboxes/{inbox_id}/messages lists captured messages, GET /inboxes/{inbox_id}/messages/{id} fetches one, and POST /inboxes/{inbox_id}/messages sends a test email. SMTP testing uses sandbox.smtp.mailtrap.io on port 2525 (default; 25/465-SSL/587 also work) with sandbox-specific credentials from the Integration tab - SMTP suits apps that already send via SMTP and just need host/port/credential changes, while the HTTP API suits new integrations and programmatic test automation. Official SDKs (Node.js, Python, PHP, Ruby, Java, .NET, CLI) expose test-mode and inbox-ID flags, so the same integration code can point at sandbox or live simply by switching credentials/mode between environments. Each sandbox also has an inbound test address (alias@inbox.mailtrap.io), with plus-addressing available to isolate test scenarios.

GET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbox_id}/messages

Integrations

Sandbox and live sending share the same account and SDK codebases but never the same tokens, hosts, or endpoints - mixing them up (using a production token for sandbox, or hitting sandbox.api.mailtrap.io expecting live delivery behavior) is the most common mistake the skill flags. Template testing pairs with Mailtrap's Handlebars-based email templates, pointed at the sandbox host with a valid inbox ID instead of the live send endpoint.

Who it's for

Developers who need to verify outbound email content and behavior - headers, HTML rendering, attachments, spam scoring, template variables - in development, staging, or CI without any risk of a real recipient receiving test mail, using the same SDK and API patterns they'll later point at live sending once ready.

FAQ

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