mailsandbox

btafoya/mailsandbox

3.2

If you are the rightful owner of mailsandbox and would like to certify it and/or have it hosted online, please leave a comment on the right or send an email to henry@mcphub.com.

MailSandbox is a versatile email testing and simulation tool designed for developers, offering a range of features including Postmark API emulation and an MCP server for AI-assisted debugging.

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MailSandbox โ€” email testing & simulation for developers

Fork of Mailpit adding Postmark API emulation and an MCP server for AI-assisted debugging.
Inspired by and grateful to the original work on Mailpit and MailHog. See Credits.

License: MIT Go Version Docker Build docker edge images Build docker images CodeQL Tests (rqlite) Build & release

Repository โ€ข Installation โ€ข Usage โ€ข Postmark API โ€ข MCP Server


MailSandbox is a small, fast, low-memory, zero-dependency, multi-platform email testing tool & API for developers.
It provides an SMTP server, modern web interface, REST API, Postmark API emulation, and an MCP server for AI-powered workflows.


Features

  • ๐Ÿš€ Lightweight โ€” single static binary or multi-arch Docker image
  • ๐ŸŒ Modern Web UI โ€” view HTML, source, headers, attachments, search & filter
  • ๐Ÿ“ฌ SMTP & POP3 servers โ€” STARTTLS/SSL/TLS, authentication, forwarding, relaying
  • ๐Ÿ” Testing tools โ€” HTML check, link check, spam score, screenshots, mobile preview
  • ๐Ÿท Tagging & filtering โ€” manual or automated (incl. plus addressing)
  • โšก Performance โ€” 100โ€“200 emails/sec, automatic pruning (default 500 emails)
  • ๐Ÿงช Chaos mode โ€” inject SMTP errors to test resilience
  • ๐Ÿ”” Integrations โ€” webhooks, browser notifications, List-Unsubscribe validation
  • ๐Ÿ†• Postmark API emulation โ€” drop-in replacement for Postmark during development
  • ๐Ÿค– MCP server โ€” AI assistants (e.g., Claude Code) can list, search, and analyze messages

Installation

The web UI runs on http://0.0.0.0:8025 and SMTP on 0.0.0.0:1025.

Script (Linux & macOS)

sudo sh < <(curl -sL https://raw.githubusercontent.com/btafoya/mailsandbox/main/install.sh)

Static binary

Download from releases, rename to mailsandbox, and add to $PATH.

Docker

docker run -d --name mailsandbox   -p 8025:8025 -p 1025:1025   btafoya/mailsandbox

Usage

List options:

mailsandbox -h

Postmark API Emulation

Enable Postmark API emulation:

mailsandbox --postmark-api --postmark-token "your-secret-token"

Environment variables:

export MP_POSTMARK_API=true
export MP_POSTMARK_TOKEN=your-secret-token
mailsandbox

Example: Node.js

const postmark = require("postmark");
const client = new postmark.ServerClient("your-secret-token");
client.apiUrl = "http://localhost:8025";
client.sendEmail({ From:"a@x.com", To:"b@y.com", Subject:"Test", TextBody:"Hello" });

Endpoints:

  • POST /email
  • POST /email/batch
  • POST /email/withTemplate

MCP Server for AI Assistants

Enable MCP server:

mailsandbox --mcp-server --mcp-transport stdio

Environment variables:

export MP_MCP_SERVER=true
export MP_MCP_TRANSPORT=stdio

Docker with MCP

docker build -t mailsandbox-with-mcp .
docker run -d --name mailsandbox   -p 127.0.0.1:8025:8025 -p 1025:1025   -e MP_MCP_SERVER=true   -e MP_MCP_TRANSPORT=stdio   -e MP_POSTMARK_API=true   -e MP_POSTMARK_TOKEN=dev-token-123   mailsandbox-with-mcp

MCP tools

  • list_messages โ€” list/filter emails
  • get_message โ€” retrieve full message
  • search_messages โ€” advanced search
  • analyze_message โ€” HTML, links, spam scoring

Migration Guide

  • Binary name renamed mailsandbox; create a symlink if you prefer mailpit.
  • Default ports unchanged: HTTP 8025, SMTP 1025.
  • APIs: REST API unchanged; Postmark & MCP are opt-in.
  • Docker: use forked image for MCP/Postmark features.

Credits & Acknowledgements

  • Mailpit โ€” by Axel Lenferna de la Motte and contributors. Original project and active development.
  • MailHog โ€” the original inspiration for mainer email testing tools.
  • MailSandbox โ€” maintained by Brian Tafoya, adding Postmark API emulation and MCP server support.

License

MailSandbox inherits the upstream license from Mailpit. See LICENSE for details.

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