邮件发送MCP服务器

Lettr MCP Server

[!IMPORTANT] This package is no longer being updated. Use Lettr's hosted MCP server instead: https://app.lettr.com/mcp

The hosted server is maintained alongside the Lettr API, so new tools and fixes land there and not here. This package keeps working, but it will not gain anything further.

Switching, with the Lettr account you sign into (OAuth):

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claude mcp add --transport http lettr https://app.lettr.com/mcp

Then authenticate when your client prompts — no API key to manage.

Switching, with an API key for CI, cron jobs and other places with no browser:

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claude mcp add --transport http lettr https://app.lettr.com/mcp \
  --header "Authorization: Bearer lttr_xxxxxxxxx"

See Connect with an API Key and the remote server setup guide for Cursor, Claude Desktop and other clients.

A few differences worth knowing before you move: tool names use snake_case there (send_email, not send-email), some parameters are named differently (contact_id rather than contactId), and the hosted server has tools this package never had — analytics, email events and API logs.

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, transactional or campaign. 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

Template purpose. A template is either transactional (the default — receipts, password resets, alerts) or campaign (marketing sent to an audience list). A campaign can only send a template whose purpose is campaign, and the purpose cannot be changed after creation, so a newsletter created with the default has to be rebuilt. Pass purpose to create-template whenever the message is going to an audience rather than to one person.

Preparation status. Imported templates render asynchronously, so a template can exist before it is sendable. list-templates and get-template report pending, ready or failed. After an update the previous render keeps serving until the new one settles, so a pending template still sends — just not yet the new content.

Folders

Folders are the only way to discover a folder_id. Without this tool the choice is to omit folder_id and accept whichever folder the API picks, or to guess an integer read out of an app URL. A folder's purpose is independent of its templates' — filing a template in a campaign folder does not make it a campaign template.

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:

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   export LETTR_API_KEY=lttr_your_key_here
   

2. Start the inspector:

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   pnpm inspector
   

3. In the browser (Inspector UI):

   • Choose stdio (launch a process).
   • Command: node
   • Args: dist/index.js
   • Env: LETTR_API_KEY=lttr_your_key_here
   • Click Connect, then use "List tools" to verify the server is working.

Resources

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

License

MIT