Email QA and staging built for developers, not screenshot farms.
Emailens replaces slow VM screenshot queues and accidental email leaks with one developer platform: instant 21-client rendering simulation, staging inboxes with an authenticated SMTP relay, OTP extraction, and MCP tooling for AI agents.
Why we built Emailens
In 2026, web developers enjoy instant HMR, modern CSS Grid and sophisticated developer tools. Yet when writing HTML emails, they are suddenly transported back to 2007: fighting Microsoft Word's rendering engine in desktop Outlook, dealing with arbitrary 102KB clipping in Gmail, and hand-coding VML ghost tables.
Traditional email testing forced two painful compromises.
-
Slow screenshot queues. Waiting 45 to 90 seconds while a remote VM booted to take a raster screenshot broke your flow for every minor CSS tweak.
-
Staging leaks and brittle CI. Staging environments accidentally blasted real users with test emails, while integration tests struggled to capture one-time passwords and magic links.
Emailens was built to end this. We parse your HTML, MJML or React Email templates directly, simulate client-specific DOM mutations in milliseconds, provide safe staging inboxes with an authenticated SMTP relay, and make email testing reproducible in CI and conversational with AI agents.
The Emailens platform today
Previews, the sandbox, the MCP server and the open-source tools.
Instant 21-client simulation
Sub-50ms AST parsing and CSS transformation across Gmail, Outlook Desktop, Apple Mail and 18 more clients. It evaluates 300 CSS and HTML features, dark mode inversion, 600px overflow and Outlook VML.
Sandbox and SMTP relay
A zero-leak staging sandbox with two ways in: @try.emailens.dev inboxes and a TLS-authenticated SMTP relay on port 2525. It extracts OTP codes and magic links for CI/CD test automation.
Explore sandboxAI-native, with an MCP server
The official @emailens/mcp server connects to Claude, Cursor and Windsurf, so coding agents can inspect email markup, diagnose client quirks and apply fixes.
View MCP setupOpen source and the developer ecosystem
An MIT-licensed core engine, a terminal CLI for CI/CD pipelines, a GitHub Action, a VS Code live preview extension, and a Figma plugin that catches rendering bugs before code is written.
How it works under the hood
Rather than a high-latency cloud browser farm, Emailens uses a client-targeting AST compiler. The engine parses raw HTML into a syntax tree, extracts the CSS rules and applies each client's mutations.
-
AST and scoped CSS
Simulates Word HTML, Blink and WebKit webmail, and vendor CSS stripping rules deterministically in under 50ms.
-
Inbound MX and SMTP on 2525
A custom SMTP relay with TLS authentication intercepts test emails, parses MIME trees and prevents real delivery.
-
Model Context Protocol
Standard MCP tools let AI agents in Cursor or Windsurf audit rendered HTML and apply framework-native fixes.
Our core principles
-
A sub-50ms feedback loop
Email QA belongs in your hot reload loop as you type, not queued behind a 90-second cloud VM screenshot farm.
-
Zero-leak staging
Staging inboxes and an authenticated SMTP relay keep test campaigns and transactional emails away from real customers.
-
Root-cause diagnostics
Not just a broken layout: the exact stripped CSS property, missing VML tag or unrendered template variable.
-
Developer and framework first
First-class ergonomics for React Email, Tailwind v4, MJML, Maizzle, Node.js, Python, Laravel and raw HTML.
-
Living standards
Every compatibility rule is grounded in vendor specifications, RFC standards and real-world email engine test suites.
-
AI-augmented workflows
Built on the Model Context Protocol so agents can analyze, audit and fix templates on demand.
The Emailens ecosystem
Founder and mission
Philippe KAM
Founder & Lead Engineer
Philippe is a software engineer passionate about developer ergonomics, web standards and automated testing. After years of wrestling with erratic email rendering across marketing automation tools and transactional workflows, he created Emailens to give developers the tooling, speed and safety they take for granted in modern web development.
Philippe
Upgrade your email testing workflow.
Simulate 21 email clients in under 50 milliseconds, or spin up a sandbox inbox for zero-leak staging.