Lettr MCP Server

The official Model Context Protocol (MCP) server for Lettr — the email API for developers. Send transactional emails, manage templates with merge tags, configure domains, and monitor webhooks — directly from any MCP client like Claude Desktop, Cursor, or Claude Code.

Why Lettr?

Lettr is a modern email sending platform built for developers. It offers a clean REST API, a powerful drag-and-drop template editor, merge tag personalization, open and click tracking, and best-in-class deliverability. Whether you're sending password resets, order confirmations, or onboarding sequences, Lettr makes it simple and reliable.

• **API Reference** — Full REST API documentation
• **Templates** — Visual email editor with merge tags
• **Domains** — Domain verification and DNS setup
• **Webhooks** — Real-time event notifications
• **Quickstart Guides** — Node.js, PHP, Laravel, Python, Go, Rust, and more

Features

• Send Emails — Send transactional emails with HTML, plain text, CC/BCC, attachments, tracking options, metadata, and tags. Supports template-based sending with merge tag substitution, scheduled delivery, and inspecting sent messages and events.
• Templates — List, create, get, update, and delete email templates. Retrieve rendered HTML and merge tags to discover which variables a template expects before sending.
• Domains — List, create, get, delete, and verify sending domains. View DNS records required for SPF, DKIM, and DMARC authentication.
• Webhooks — List, create, get, update, and delete webhook configurations for real-time email event notifications.
• Projects — List the projects available to your team so you can target template and email tools at a specific project.
• Audience — Manage contacts, lists, subscription topics, custom properties, and segments. Create and update contacts (with double opt-in), attach contacts to lists and topics, bulk import, and build segments from match conditions.
• System — Health check and API key validation for client setup and diagnostics.

Setup

1. Create a free Lettr account

2. Create an API key in your dashboard

3. Verify your domain to send emails to any recipient

Usage

Claude Code

claude mcp add lettr -e LETTR_API_KEY=lttr_xxxxxxxxx -- npx -y lettr-mcp

Cursor

Open the command palette and choose "Cursor Settings" > "MCP" > "Add new global MCP server".

{
  "mcpServers": {
    "lettr": {
      "command": "npx",
      "args": ["-y", "lettr-mcp"],
      "env": {
        "LETTR_API_KEY": "lttr_xxxxxxxxx"
      }
    }
  }
}

Claude Desktop

Open Claude Desktop settings > "Developer" tab > "Edit Config".

{
  "mcpServers": {
    "lettr": {
      "command": "npx",
      "args": ["-y", "lettr-mcp"],
      "env": {
        "LETTR_API_KEY": "lttr_xxxxxxxxx"
      }
    }
  }
}

Options

You can pass additional arguments to configure the server:

• `--key`: Your Lettr API key (alternative to `LETTR_API_KEY` env var)
• `--sender`: Default sender email address from a verified domain
• `--reply-to`: Default reply-to email address

Environment variables:

• `LETTR_API_KEY`: Your Lettr API key (required)
• `SENDER_EMAIL_ADDRESS`: Default sender email address from a verified domain (optional)
• `REPLY_TO_EMAIL_ADDRESS`: Default reply-to email address (optional)

> Note: If you don't provide a sender email address, the MCP server will ask for one each time you send an email.

Available Tools

Emails

Templates

Domains

Webhooks

Projects

Audience

System

Local Development

1. Clone and build:

git clone https://github.com/nicholasgriffintn/lettr-mcp.git
cd lettr-mcp
pnpm install
pnpm run build

2. Use the local build in your MCP client:

{
  "mcpServers": {
    "lettr": {
      "command": "node",
      "args": ["ABSOLUTE_PATH_TO_PROJECT/dist/index.js"],
      "env": {
        "LETTR_API_KEY": "lttr_xxxxxxxxx"
      }
    }
  }
}

Testing with MCP Inspector

> Make sure you've built the project first (see Local Development above).

1. Set your API key:

export LETTR_API_KEY=lttr_your_key_here

2. Start the inspector:

pnpm inspector

3. In the browser (Inspector UI):

Resources

• Lettr Website
• API Documentation
• MCP Setup Guide
• MCP Tools Reference
• Template Language
• DNS Setup Guides
• Knowledge Base

License

MIT