Agent skill

Mailtrap Testing With Sandbox

by sickn33 in sickn33/agentic-awesome-skills

Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests.

MITAuto-check passedProductivity & Automation

Install Mailtrap Testing With Sandbox

skills CLI
$ npx skills add sickn33/agentic-awesome-skills --skill mailtrap-testing-with-sandbox -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install sickn33/agentic-awesome-skills mailtrap-testing-with-sandbox --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/sickn33/agentic-awesome-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/mailtrap-testing-with-sandbox .claude/skills/mailtrap-testing-with-sandbox && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
mailtrap-testing-with-sandbox
GitHub stars
47k
Used in
1 other repo
Token cost
~1.9k tokens
SKILL.md length
678 words
Files
1
Skills in repo
1,493
Repo updated
First seen
Licence
MIT

At a glance

Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests.

  • Tasks that involve Email management
  • SKILL.md covers Overview, When to use, When not to use and Quick reference, plus 1 more section
  • Reaches mailtrap.io and sandbox.api.mailtrap.io; needs MAILTRAP_SANDBOX_API_TOKEN and MAILTRAP_API_TOKEN
  • Tasks that involve Transactional email

What it does

Mailtrap Testing With Sandbox is an agent skill from sickn33/agentic-awesome-skills. Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests.

Its SKILL.md is about 1.9k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Productivity & Automation, covering Email management and Transactional email. The repository describes itself as: AAS Core is the local, agent-first control plane for complete catalog discovery, agent-owned selection, stack validation, and planning, backed by 2,400+ agentic skills. Includes… The licence is MIT.

When your agent uses it

  • Tasks that involve Email management
  • Tasks that involve Transactional email

Example prompts

  • “/mailtrap-testing-with-sandbox”

Requirements

  • Node.js
  • A credential in MAILTRAP_SANDBOX_API_TOKEN
  • A credential in MAILTRAP_API_TOKEN

What it can do on your machine

Read from SKILL.md and the folder at commit 680176d. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    Hosts in commands or code, which the agent is likely to contact:

    • mailtrap.io
    • sandbox.api.mailtrap.io

    Also links to:

    • docs.mailtrap.io
    • github.com

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names these keys or tokens, usually read from environment variables:

    • MAILTRAP_SANDBOX_API_TOKEN
    • MAILTRAP_API_TOKEN

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Mailtrap Testing With Sandbox loads about 1.9k tokens when it runs. Until then it costs about 40 tokens; SKILL.md has 678 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~40
When it runs · the whole SKILL.md, loaded when a task matches
~1.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from sickn33/agentic-awesome-skills at commit 680176d, republished under its MIT licence (© sickn33). 678 words, ~1,937 tokens.

Download SKILL.mdSave it as .claude/skills/mailtrap-testing-with-sandbox/SKILL.md (or your agent's skills folder).
name
mailtrap-testing-with-sandbox
description
Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests.
risk
safe
source
community
date_added
2026-06-19

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
ServiceSend mail URLAuth 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)
SettingValue
Hostsandbox.smtp.mailtrap.io
Ports2525 (default), 25, 465 (SSL), 587
Username / PasswordPer 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.
Show full SKILL.md (298 more words)Show less
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:

OperationURLReference
List sandboxesGET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxesSandboxes API
List messagesGET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbox_id}/messagesMessages
Fetch a messageGET https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbox_id}/messages/{id}Message details
Send test emailPOST https://mailtrap.io/api/accounts/$MAILTRAP_ACCOUNT_ID/inboxes/{inbox_id}/messagesSend test emails

For template testing, see the Integration tab of your template and Handlebars.

SDKs

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:

Common mistakes
MistakeFix/Explanation
Expecting real delivery from sandboxMail in the sandbox is never delivered to recipients
Using production API token for sandboxUse a token with proper sandbox/testing scope, granting access to the target inbox
Forgetting inbox id parameterAlways supply the inbox id (from UI or Integration tab) to associate messages with the correct inbox
Mixing sandbox and transactional endpointsTesting API (sandbox.api.mailtrap.io) is not the same as send.api.mailtrap.io (live sending)!
Sandbox email address

Each sandbox (test inbox) has an address like alias@inbox.mailtrap.io for inbound tests; plus-addressing can help isolate scenarios. See Email address per sandbox for limits and behavior.

Limitations

  • This skill covers sandbox usage patterns; use Mailtrap's current API docs for full endpoint schemas.

© sickn33, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/mailtrap-testing-with-sandbox of sickn33/agentic-awesome-skills.

Open the folder on GitHubat commit 680176d

Used in 1 other repository

We found 5 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 1 other GitHub owner. This page covers the copy in sickn33/agentic-awesome-skills, which our catalogue first saw on October 7, 2026.

Compare with similar skills

Mailtrap Testing With Sandbox next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Mailtrap Testing With Sandbox compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Mailtrap Testing With Sandbox this skillsickn33/agentic-awesome-skills47k1 repos~1.9kAutomated safety check: PassMIT
Gmail Emailopen-gitagent/gitagent713—~235Automated safety check: NotesMIT
Tethertokencanopy/e2a193—~4.7kAutomated safety check: PassApache-2.0
E2atokencanopy/e2a193—~4.7kAutomated safety check: PassApache-2.0
Inbox Placement Monitoraaron-he-zhu/aaron-marketing-skills2.9k2 repos~3.6kAutomated safety check: PassApache-2.0
Email Deliverability Auditgrowthenginenowoslawski/coldoutboundskills751—~3.4kAutomated safety check: PassMIT

Similar skills

  • Gmail Email

    open-gitagent/gitagent

    Send emails via Gmail SMTP using App Password authentication.

    713 GitHub stars~235 tokensUpdated today
    Productivity & AutomationAuto-check: notes
  • Tether

    tokencanopy/e2a

    Beta — Stay in the loop over email during a long-running coding session.

    193 GitHub stars~4.7k tokensUpdated 3 days ago
    Productivity & AutomationAuto-check passed
  • E2a

    tokencanopy/e2a

    A skill your agent uses when operating an already-connected e2a inbox over MCP: reading, composing, sending, replying, forwarding, handling attachments, managing contacts/outreach, scheduling mail…

    193 GitHub stars~4.7k tokensUpdated 3 days ago
    Productivity & AutomationAuto-check passed
  • Inbox Placement Monitor

    aaron-he-zhu/aaron-marketing-skills

    A skill your agent uses when the user asks to "track where my emails are actually landing after I send", "read my seed-list inbox vs spam vs promotions results", "trend my Gmail Postmaster /…

    2.9k GitHub starsUsed in 2 repos~3.6k tokens
    Productivity & AutomationAuto-check passed
  • Email Deliverability Audit

    growthenginenowoslawski/coldoutboundskills

    Diagnostic audit for a running cold email program. An agent skill from growthenginenowoslawski/coldoutboundskills.

    751 GitHub stars~3.4k tokensUpdated 3 days ago
    Backend & APIsAuto-check passed
  • Himalaya Email CLI

    Prismer-AI/PrismerCloud

    Operates a mailbox from the terminal with the external Himalaya CLI over IMAP, SMTP, Notmuch or Sendmail, separate from any built-in email gateway adapter.

    1.6k GitHub starsUsed in 2 repos~2.3k tokens
    Backend & APIsAuto-check passed

More from sickn33/agentic-awesome-skills

All 1,493 skills in this repo
  • Liuguang Banlan UI

    sickn33/agentic-awesome-skills

    Implements an interface in one of two named color modes, iridescent white or colorful black, from a parameterized starter that reports measured color intensity.

    47k GitHub starsUsed in 1 repo~2.5k tokens
    Auto-check passed
  • User Thoughts Memory

    sickn33/agentic-awesome-skills

    Saves a user's project decisions, rules and preferences into a project-local mdbase so later sessions and other agents can recover the intent.

    47k GitHub starsUsed in 1 repo~2.5k tokens
    Auto-check passed
  • Using LWC Memory and Graphs

    sickn33/agentic-awesome-skills

    Keeps project decisions, research and verified results available across coding-agent sessions through LWC memory, a document Wiki graph and a CodeGraph code index.

    47k GitHub starsUsed in 1 repo~2k tokens
    Auto-check passed
  • Find Complementary Founders

    sickn33/agentic-awesome-skills

    Guides an agent through assessing its own owner for cofounder fit, publishing an approved profile, and ranking complementary profiles other agents published for their owners.

    47k GitHub starsUsed in 1 repo~4.8k tokens
    Auto-check passed
  • Whatsapp Cloud API

    sickn33/agentic-awesome-skills

    Integracao com WhatsApp Business Cloud API (Meta). An agent skill from sickn33/agentic-awesome-skills.

    47k GitHub starsUsed in 2 repos~4.5k tokens
    Auto-check passed
  • Cline Pilot

    sickn33/agentic-awesome-skills

    Acts as a proxy for the Cline CLI, dispatching coding tasks one at a time, monitoring runs by hard evidence, relaying decisions to you and learning per-project preferences.

    47k GitHub starsUsed in 1 repo~4.6k tokens
    Auto-check passed

Questions about Mailtrap Testing With Sandbox

What does Mailtrap Testing With Sandbox do?

Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests. Mailtrap Testing With Sandbox is an agent skill from sickn33/agentic-awesome-skills. Capture outbound email in Mailtrap Email Sandbox for development, staging, CI, HTML inspection, spam checks, and fake inbox tests.

When should I use Mailtrap Testing With Sandbox?

Mailtrap Testing With Sandbox fits situations like: tasks that involve Email management; tasks that involve Transactional email.

How do I install Mailtrap Testing With Sandbox in Claude Code?

Run `npx skills add sickn33/agentic-awesome-skills --skill mailtrap-testing-with-sandbox -a claude-code`. Or copy the skill folder (skills/mailtrap-testing-with-sandbox in sickn33/agentic-awesome-skills) into .claude/skills/mailtrap-testing-with-sandbox in your project. Claude Code loads it when a task matches its description.

How do I install Mailtrap Testing With Sandbox in Codex?

Run `npx skills add sickn33/agentic-awesome-skills --skill mailtrap-testing-with-sandbox -a codex`. Or copy the skill folder (skills/mailtrap-testing-with-sandbox in sickn33/agentic-awesome-skills) into .agents/skills/mailtrap-testing-with-sandbox in your project. Codex loads it when a task matches its description.

Can I use Mailtrap Testing With Sandbox in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add sickn33/agentic-awesome-skills --skill mailtrap-testing-with-sandbox -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/mailtrap-testing-with-sandbox, .gemini/skills/mailtrap-testing-with-sandbox, .github/skills/mailtrap-testing-with-sandbox and .opencode/skills/mailtrap-testing-with-sandbox in your project.

What does Mailtrap Testing With Sandbox need to run?

Going by SKILL.md and its folder, Mailtrap Testing With Sandbox needs credentials named MAILTRAP_SANDBOX_API_TOKEN and MAILTRAP_API_TOKEN. Our summary lists: Node.js; A credential in MAILTRAP_SANDBOX_API_TOKEN; A credential in MAILTRAP_API_TOKEN.

Does Mailtrap Testing With Sandbox access the network?

SKILL.md names 4 domains. In commands or code: mailtrap.io and sandbox.api.mailtrap.io; the agent is likely to contact these when it follows the instructions. As links in the text: docs.mailtrap.io and github.com. This is read from the text; nothing was executed.

Is Mailtrap Testing With Sandbox safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Mailtrap Testing With Sandbox use?

Mailtrap Testing With Sandbox is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Mailtrap Testing With Sandbox use?

About 1.9k tokens (SKILL.md is roughly 7.7k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Mailtrap Testing With Sandbox?

Skills that share tags, products or a category with Mailtrap Testing With Sandbox: Gmail Email (open-gitagent/gitagent, 713 stars), Tether (tokencanopy/e2a, 193 stars), E2a (tokencanopy/e2a, 193 stars) and Inbox Placement Monitor (aaron-he-zhu/aaron-marketing-skills, 2.9k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Mailtrap Testing With Sandbox?

sickn33 (a GitHub user) maintains it in sickn33/agentic-awesome-skills, which has 47,379 GitHub stars. The repository holds 1,493 skills in this directory. The repository was last updated on October 9, 2026.

Source: sickn33/agentic-awesome-skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.