Testing with Mailtrap Email Sandbox
Overview
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 mailtrap-sending-emails) for current sandbox mode options, inbox id, and constructor flags. Do not rely on memory.
Related skills: mailtrap-sending-emails (live sending hosts and streams).
When to use
- You want no real delivery: dev, staging, CI, or demos where mail must stay in a test inbox.
- You need to inspect what was sent: bodies, headers, attachments, or basic checks (e.g. spam report) via Sandbox / Testing API or the UI.
- You are automating tests against captured mail.
- You will only change SMTP settings so an existing app sends into a sandbox—no need for a framework-by-framework tutorial from this skill.
When not to use
- Live sends to real recipients (
mailtrap-sending-emails).
- For full framework setup guides or detailed API references, link users to Mailtrap's Integration tab for SMTP/API details and the API docs for specifics—don't cover every framework or API field here.
Quick reference
API base
| Service |
Send mail URL |
Auth header examples |
| Email Testing API (REST) |
https://sandbox.api.mailtrap.io/api/send/{inbox_id} |
Authorization: Bearer $MAILTRAP_SANDBOX_API_TOKEN |
Tokens and account_id
Sandbox uses a separate token ($MAILTRAP_SANDBOX_API_TOKEN, Testing/Sandbox scope) — never reuse the live $MAILTRAP_API_TOKEN. The account_id in the example endpoints below is resolved at runtime via GET https://mailtrap.io/api/accounts. Store tokens in environment variables or a secrets manager.
When to use API vs SMTP
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.
SMTP settings (sandbox)
| 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.
Key parameters
- Inbox ID: Every sandbox (test inbox) has a unique inbox id, visible in the UI URL and needed for sending or REST API operations.
- Token scope: Use a token with permissions for the relevant project and test inbox.
Typical use cases
- Capture all outbound mail in dev, test, or staging (no real recipients).
- View, validate, and assert message headers, bodies, HTML, attachments, or spam score.
- Run integration or CI checks that read from the Email Sandbox API.
- Test Mailtrap templates by pointing API or SDK/SMTP at
sandbox.api.mailtrap.io / sandbox.smtp.mailtrap.io with a valid inbox id.
Example API paths
Use API docs for details, but typical endpoints include:
1---2name: mailtrap-testing-with-sandbox3description: Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests.4---5
6
7# Testing with Mailtrap Email Sandbox
8
9## Overview
10
11**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.
12
13**Before generating SDK code:** read the README of the relevant SDK repository (see `mailtrap-sending-emails`) for current sandbox mode options, **inbox id**, and constructor flags. Do not rely on memory.
14
15**Related skills:** `mailtrap-sending-emails` (live sending hosts and streams).
16
17## When to use
18
19- You want **no real delivery**: dev, staging, CI, or demos where mail must stay in a **test inbox**.
20- You need to **inspect** what was sent: bodies, headers, attachments, or basic checks (e.g. spam report) via **Sandbox / Testing API** or the **UI**.
21- You are **automating** tests against captured mail.
22- You will **only change SMTP settings** so an existing app sends into a sandbox—no need for a framework-by-framework tutorial from this skill.
23
24## When not to use
25
26- **Live** sends to real recipients (`mailtrap-sending-emails`).
27- For full framework setup guides or detailed API references, link users to Mailtrap's Integration tab for SMTP/API details and the [API docs](https://docs.mailtrap.io/developers/) for specifics—don't cover every framework or API field here.
28
29## Quick reference
30
31### API base
32
33| Service | Send mail URL | Auth header examples |
34| ------------------------ | ----------------------------------------------------- | ------------------------------------------------- |
35| Email Testing API (REST) | `https://sandbox.api.mailtrap.io/api/send/{inbox_id}` | `Authorization: Bearer $MAILTRAP_SANDBOX_API_TOKEN` |
36
37### Tokens and account_id
38
39Sandbox uses a **separate** token (`$MAILTRAP_SANDBOX_API_TOKEN`, Testing/Sandbox scope) — never reuse the live `$MAILTRAP_API_TOKEN`. The `account_id` in the example endpoints below is resolved at runtime via `GET https://mailtrap.io/api/accounts`. Store tokens in environment variables or a secrets manager.
40
41### When to use API vs SMTP
42
43Use **SMTP** when testing apps that already send mail via SMTP (just update the host, port, and credentials).
44Use the **HTTP API** when building new integrations or your app can make HTTP requests; it's better for programmatic testing and automation.
45
46### SMTP settings (sandbox)
47
48| Setting | Value |
49| ------------------- | --------------------------------------------------------------------------- |
50| Host | `sandbox.smtp.mailtrap.io` |
51| Ports | 2525 (default), 25, 465 (SSL), 587 |
52| Username / Password | Per **sandbox** credentials from the **Integration** tab in the Mailtrap UI |
53
54**Never use sandbox credentials or endpoints in production. Messages will only be captured in the sandbox, not delivered.**
55
56### Key parameters
57
58- **Inbox ID**: Every sandbox (test inbox) has a unique **inbox id**, visible in the UI URL and needed for sending or REST API operations.
59- **Token scope**: Use a token with permissions for the relevant project and test inbox.
60
61### Typical use cases
62
63- Capture all outbound mail in dev, test, or staging (no real recipients).
64- View, validate, and assert message headers, bodies, HTML, attachments, or spam score.
65- Run integration or CI checks that read from the Email Sandbox API.
66- Test Mailtrap **templates** by pointing API or SDK/SMTP at `sandbox.api.mailtrap.io` / `sandbox.smtp.mailtrap.io` with a valid inbox id.
67
68### Example API paths
69
70Use [API docs](https://docs.mailtrap.io/developers/) for details, but typical endpoints include:
71
72| Operation | URL | Reference |
73| --------------- | -------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------- |
74| List sandboxes | `GET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes` | [Sandboxes API](https://docs.mailtrap.io/developers/email-sandbox/sandboxes-inboxes.md) |
75| List messages | `GET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbox_id}/messages` | [Messages](https://docs.mailtrap.io/developers/email-sandbox/messages.md) |
76| Fetch a message | `GET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbox_id}/messages/{id}` | [Message details](https://docs.mailtrap.io/developers/email-sandbox/messages.md) |
77| Send test email | `POST https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbo
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