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.
• 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

Tool	Description
send-email	Send a transactional email with HTML, plain text, templates, attachments, tracking, and personalization
list-emails	List recently sent emails (cursor-paginated, with recipient and date filters)
list-email-events	List email events (delivery, bounce, click, open, …) with filters by type, recipient, transmission, and date range
get-email-detail	Retrieve the full delivery timeline for a single transmission by request ID
schedule-email	Schedule a transactional email for future delivery (5+ minutes ahead, within 3 days)
get-scheduled-email	Get the state and events of a scheduled transmission
cancel-scheduled-email	Cancel a scheduled transmission before it is sent

Templates

Tool	Description
list-templates	List email templates with pagination
get-template	Get full template details including HTML content
create-template	Create a new template with HTML or visual editor JSON
update-template	Update template name and/or content (creates new version)
delete-template	Permanently delete a template and all versions
get-merge-tags	Discover merge tag variables a template expects
get-template-html	Retrieve a template's rendered HTML, subject, and merge tags by project ID and slug

Domains

Tool	Description
list-domains	List all sending domains and their verification status
create-domain	Register a new sending domain
get-domain	Get domain details with DNS records
delete-domain	Remove a sending domain
verify-domain	Trigger DNS verification for a domain

Webhooks

Tool	Description
list-webhooks	List all webhook configurations
get-webhook	Get webhook details and delivery status
create-webhook	Create a new webhook subscription with auth and event-type selection
update-webhook	Update an existing webhook (name, URL, auth, events, active flag)
delete-webhook	Delete a webhook subscription

Projects

Tool	Description
list-projects	List projects owned by the team — useful for discovering project IDs

System

Tool	Description
health-check	Check the Lettr API health status
auth-check	Validate the configured API key and return the team ID

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):

   • 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