Open-Source Testing · maildev

maildev

MailDev is a lightweight Node.js-based SMTP server with a web UI for intercepting and viewing emails during development. It eliminates the need to send test emails to real addresses and integrates with Docker, REST APIs, and MCP for AI agent integration.

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Source: GitHub — github.com/maildev/maildev

5.9k

GitHub stars

551

Forks

TypeScript

Primary language

MIT

License (OSI-approved)

Key facts

Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.

Field	Value
Repository	maildev/maildev
Owner	maildev
Primary language	TypeScript
License	MIT — OSI-approved
Stars	5.9k
Forks	551
Open issues	56
Latest release	[email protected] (2026-07-06)
Last updated	2026-07-07
Source	https://github.com/maildev/maildev

What maildev is

Built in TypeScript, MailDev runs a local SMTP server (default port 1025) that captures outgoing mail and displays it via a web interface (port 1080). It supports optional TLS/SSL, authentication, outgoing relay to real SMTP servers, and programmatic access via Node.js API and REST endpoints. Version 3.0-rc.1 represents a complete rewrite.

Quickstart

Get the maildev source

Clone the repository and explore it locally.

terminalbash

1git clone https://github.com/maildev/maildev.git2cd maildev3# follow the project's README for install & configuration

Need it deployed, integrated, or customized instead? DEV.co ships production installs.

Best use cases

Development email testing

Capture and inspect email output from your application without sending real emails, speeding up development cycles and avoiding accidental customer contact.

CI/CD email validation

Integrate into automated test suites via REST API or Node.js API to validate email generation, formatting, and content in integration tests.

Debugging email workflows

Quickly inspect raw email content, headers, attachments, and rendering to identify issues in transactional email systems before relay to production SMTP.

Implementation considerations

Version 3.0-rc.1 is a release candidate; production use of v2 is more stable. Evaluate pre-release stability for your workflow.
Requires Node.js runtime; deploy via npm, Docker, or programmatically as a library in your application.
Default ports (1025 SMTP, 1080 web) may conflict; use CLI flags or environment variables to bind to different ports/IPs.
Mail directory option allows persistence across restarts; otherwise mail is lost on stop.
MCP server integration (--mcp) enables Claude and other AI agents to query and extract email tokens/links programmatically.

When to avoid it — and what to weigh

Production email delivery required — MailDev is for development only. Do not configure it to accept production traffic; use it only in isolated dev/test environments.
High-volume email inspection — Not designed for performance under heavy mail load; best suited for small to moderate development and testing scenarios.
Persistent production email archive — Mail is stored in-memory or in a local directory; not suitable as a reliable long-term email store for compliance or audit trails.
Complex authentication schemes — Supports basic SMTP auth and HTTP credentials, but lacks advanced auth integrations (OAuth, LDAP, etc.).

License & commercial use

MIT License. Permits unrestricted use, modification, and distribution in commercial and private projects, provided the license text and copyright notice are included.

MIT is a permissive OSI-approved license suitable for commercial use. No restrictions on commercial deployment of applications that use MailDev. However, review MIT terms to ensure license attribution is included in your distribution.

DEV.co evaluation signals

Editorial assessment — not user reviews. Directional, with an explicit confidence level.

Signal	Assessment
Maintenance	Active
Documentation	Adequate
License clarity	Clear
Deployment complexity	Low
DEV.co fit	Strong
Assessment confidence	High

Security considerations

MailDev is a development tool; assume network isolation. SMTP and web interfaces listen on configurable IPs; bind to localhost (127.0.0.1) or private networks only. Optional HTTP auth (--web-user/--web-pass) protects the web UI. Incoming SMTP can require credentials. TLS/SSL support available for SMTP and HTTPS web UI. Do not expose to untrusted networks. No mention of vulnerability disclosure process or security audit history.

Alternatives to consider

MailHog

Similar SMTP + web UI tool; written in Go; may offer different performance or deployment characteristics. Mature and widely used.

Ethereal Email (Mailtrap)

Cloud-based SMTP service with web UI; no local infrastructure required, but requires account and internet connectivity. Better for team collaboration.

smtp4dev

.NET-based alternative with GUI; cross-platform; similar feature set to MailDev. Choice depends on tech stack familiarity.

Software development agency

Build on maildev with DEV.co software developers

Install MailDev via npm or Docker to eliminate real test email sends and debug email workflows faster. MIT licensed and open-source.

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maildev FAQ

Can I use MailDev to send real emails?

Only via the optional outgoing/relay feature, which must be explicitly configured with real SMTP credentials. By default, MailDev only intercepts and displays emails in the web UI.

Does MailDev persist emails across restarts?

Not by default; emails are stored in memory and lost on stop. Use the --mail-directory option to persist emails to disk.

Can I integrate MailDev into my test suite?

Yes, via REST API or by importing the Node.js API directly into your test code. Query emails, verify content, and extract tokens programmatically.

Is version 3.0 production-ready?

Version 3.0-rc.1 is a release candidate (preview). For stability, the docs recommend v2 if you encounter issues. Evaluate based on your risk tolerance.

Work with a software development agency

DEV.co is a software development agency delivering custom software development services to companies building on open source. Our software developers and web developers design, integrate, and ship production systems — spanning web development, APIs, AI, data, and cloud. If maildev is part of your open-source testing roadmap, our team can implement, customize, migrate, and maintain it.

Start Testing Emails Locally

Install MailDev via npm or Docker to eliminate real test email sends and debug email workflows faster. MIT licensed and open-source.

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