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

| 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 |

Audience

| Tool | Description | |------|-------------| | list-audience-lists | List audience (contact) lists with pagination | | create-audience-list | Create a new audience list | | get-audience-list | Get a single list and its contact count | | update-audience-list | Rename an audience list | | delete-audience-list | Delete an audience list | | bulk-delete-audience-lists | Delete up to 50 lists in one call | | list-audience-contacts | List contacts with search, status, list, and segment filters | | get-audience-contact | Get a contact with its properties, lists, and topics | | create-audience-contact | Create a contact, optionally with double opt-in | | bulk-create-audience-contacts | Create many contacts from a list of emails | | update-audience-contact | Update a contact's email, status, or properties | | delete-audience-contact | Delete a contact | | attach-contact-to-list | Add a contact to a list | | detach-contact-from-list | Remove a contact from a list | | subscribe-contact-to-topic | Subscribe a contact to a topic | | unsubscribe-contact-from-topic | Unsubscribe a contact from a topic | | bulk-attach-contacts-to-lists | Attach many contacts to many lists at once | | bulk-detach-contacts-from-lists | Detach many contacts from many lists at once | | list-audience-topics | List subscription topics with pagination | | create-audience-topic | Create a subscription topic | | get-audience-topic | Get a single topic | | update-audience-topic | Update a topic's name, description, or visibility | | delete-audience-topic | Delete a subscription topic | | list-audience-properties | List custom contact properties | | create-audience-property | Define a new custom property | | get-audience-property | Get a single property | | update-audience-property | Update a property's fallback value | | delete-audience-property | Delete a custom property | | list-audience-segments | List segments, optionally filtered by list | | create-audience-segment | Create a segment from match conditions | | get-audience-segment | Get a single segment and its conditions | | update-audience-segment | Update a segment's name, list, or conditions | | delete-audience-segment | Delete a segment |

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