Use when capturing outbound email in development or staging without delivering to real recipients, inspecting HTML or headers, running spam or structure checks, or automating tests against a fake inbox. Use when testing outgoing mail from an app without committing to a production ESP yet. Use when using Mailtrap Email Sandbox, Sandbox API, or sandbox-mode sending.
Email Sandbox captures mail in sandboxes (test inboxes)—a test environment where messages are not delivered to real recipients. You can send to sandboxes using our SDKs, HTTP API, or SMTP, depending on your needs.
Before generating SDK code: read the README of the relevant SDK repository (see sending-emails) for current sandbox mode options, inbox id, and constructor flags. Do not rely on memory.
Related skills: sending-emails (live sending hosts and streams), using-email-templates (preview template sends in sandbox).
sending-emails).| Service | Send mail URL | Auth header examples |
|---|---|---|
| Email Testing API (REST) | https://sandbox.api.mailtrap.io/api/send/{inbox_id} | Authorization: Bearer YOUR_SANDBOX_API_TOKEN |
Tokens are created under Settings > API Tokens. Use a token with Testing/Sandbox scope to access sandbox resources or send into a sandbox.
Use SMTP when testing apps that already send mail via SMTP (just update the host, port, and credentials). Use the HTTP API when building new integrations or your app can make HTTP requests; it's better for programmatic testing and automation.
| Setting | Value |
|---|---|
| Host | sandbox.smtp.mailtrap.io |
| Ports | 2525 (default), 25, 465 (SSL), 587 |
| Username / Password | Per sandbox credentials from the Integration tab in the Mailtrap UI |
Never use sandbox credentials or endpoints in production. Messages will only be captured in the sandbox, not delivered.
sandbox.api.mailtrap.io / sandbox.smtp.mailtrap.io with a valid inbox id.Use API docs for details, but typical endpoints include:
| Operation | URL | Reference |
|---|---|---|
| List sandboxes | GET https://mailtrap.io/api/accounts/{account_id}/inboxes | Sandboxes API |
| List messages | GET https://mailtrap.io/api/accounts/{account_id}/inboxes/{inbox_id}/messages | Messages |
| Fetch a message | GET https://mailtrap.io/api/accounts/{account_id}/inboxes/{inbox_id}/messages/{id} | Message details |
| Send test email | POST https://mailtrap.io/api/accounts/{account_id}/inboxes/{inbox_id}/messages | Send test emails |
For template testing, see the Integration tab of your template and Handlebars.
Official Mailtrap SDKs support sandbox/inbox operations and provide flags or methods to set test mode and inbox id. This allows you to use the same integration for both live sending and sandbox testing—simply change the mode or credentials depending on your environment (development, staging, or production). For install commands and language coverage, see Mailtrap developer documentation. Repository READMEs have the latest sandbox options:
| Mistake | Fix/Explanation |
|---|---|
| Expecting real delivery from sandbox | Mail in the sandbox is never delivered to recipients |
| Using production API token for sandbox | Use a token with proper sandbox/testing scope, granting access to the target inbox |
| Forgetting inbox id parameter | Always supply the inbox id (from UI or Integration tab) to associate messages with the correct inbox |
| Mixing sandbox and transactional endpoints | Testing API (sandbox.api.mailtrap.io) is not the same as send.api.mailtrap.io (live sending)! |
Each sandbox (test inbox) has an address like [email protected] for inbound tests; plus-addressing can help isolate scenarios. See Email address per sandbox for limits and behavior.