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Lettio MCP

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Private, EU-hosted email for AI agents over JMAP: read, search, reply, organize, send.

Source code Documentation

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

Remote (streamable-http)
Claude Code 
claude mcp add --transport http lettio-mcp 'https://mcp.lettio.eu/mcp'
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "lettio-mcp": {
            "type": "http",
            "url": "https://mcp.lettio.eu/mcp"
        }
    }
}
NPM package @lettio/mcp
Claude Code 
claude mcp add lettio-mcp -e 'LETTIO_USERNAME=<LETTIO_USERNAME>' -e 'LETTIO_PASSWORD=<your lettio_password>' -e 'LETTIO_HOST=<LETTIO_HOST>' -- npx -y @lettio/mcp@0.1.2
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "lettio-mcp": {
            "command": "npx",
            "args": [
                "-y",
                "@lettio/mcp@0.1.2"
            ],
            "env": {
                "LETTIO_USERNAME": "<LETTIO_USERNAME>",
                "LETTIO_PASSWORD": "<your lettio_password>",
                "LETTIO_HOST": "<LETTIO_HOST>"
            }
        }
    }
}

Environment variables

  • LETTIO_USERNAME required Full email address of the Lettio mailbox, e.g. you@yourcompany.eu.
  • LETTIO_PASSWORD required secret App password for the mailbox.
  • LETTIO_HOST Mail host. Defaults to https://mail.lettio.eu.

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. Lettio MCP
  2. Tools
  3. Requirements
  4. Use with Claude Desktop
  5. Configuration
  6. Security
  7. Run from source
  8. License

Lettio MCP

Let your AI assistant read, search and send email from a private, EU-hosted mailbox.

Lettio MCP is a Model Context Protocol server that connects an AI agent (Claude, Cursor, and any other MCP client) to a Lettio mailbox over JMAP. Your assistant can triage your inbox, find a message, and send a reply — without your email ever leaving Europe.

  • 🇪🇺 European by default — talks to your own EU-hosted mailbox, no third‑party middleman.
  • 🔒 Safe sending — the server can only ever send as the mailbox it is signed in to. It cannot be tricked into sending from another address.
  • 📬 Everything an agent needs — list, search, read and send, over the open JMAP standard.
  • 👥 One or many mailboxes — configure a single account or several.

Prefer nothing to install? Lettio also runs as a hosted, OAuth‑secured MCP server at https://mcp.lettio.eu/mcp — add that URL in your client and sign in. This npm package is the local / self‑hosted option for people who want to run it on their own machine.

Tools

ToolWhat it does
list_accountsList the mailboxes this server is configured for.
list_mailboxesList folders in an account, with message and unread counts.
list_recent_emailsMost recent messages in a mailbox (defaults to the inbox).
search_emailsFree‑text search across sender, subject and body.
read_emailFull content of one message by id.
send_emailSend a plain‑text email as the signed‑in mailbox.
reply_emailReply in‑thread (keeps the conversation), optionally reply‑all.
set_read_statusMark a message read or unread.
flag_emailFlag (star) or unflag a message.
move_emailMove to a folder — archive, trash (reversible), or a folder name.

Requirements

  • Node.js 18 or newer.
  • A Lettio mailbox and an app password for it (use a dedicated app password, not your main login).

Use with Claude Desktop

Add this to your claude_desktop_config.json:

{
  "mcpServers": {
    "lettio": {
      "command": "npx",
      "args": ["-y", "@lettio/mcp"],
      "env": {
        "LETTIO_USERNAME": "you@yourcompany.eu",
        "LETTIO_PASSWORD": "your-app-password"
      }
    }
  }
}

Restart Claude Desktop; the Lettio tools appear in the tools menu.

Configuration

Configured entirely through environment variables.

Single mailbox
VariableRequiredDescription
LETTIO_USERNAMEyesFull email address, e.g. you@yourcompany.eu.
LETTIO_PASSWORDyesMailbox app password.
LETTIO_HOSTnoMail host. Defaults to https://mail.lettio.eu.
LETTIO_ACCOUNT_NAMEnoFriendly name for the account (default: the username).
Several mailboxes

Set LETTIO_ACCOUNTS to a JSON array and omit the single‑account variables:

[
  { "name": "work", "username": "you@yourcompany.eu", "password": "app-password" },
  { "name": "sales", "username": "sales@yourcompany.eu", "password": "app-password" }
]

Then pass account: "work" to any tool to choose which mailbox to use.

Security

Sending is deliberately constrained. Before it sends, the server asks the mail host for the identities the signed‑in mailbox is allowed to use and requires one that matches the login address. The From header and the SMTP envelope MAIL FROM are both pinned to that address. There is no parameter for choosing a different sender, so an agent can never send "from" a foreign or arbitrary mailbox. Credentials are read from the environment, kept only in memory, and never logged.

Run from source

npm install
npm run build
LETTIO_USERNAME=you@yourcompany.eu LETTIO_PASSWORD=app-password npm start

License

MIT © Valmia Solutions s.r.o.

Frequently asked questions

What is Lettio MCP?

Private, EU-hosted email for AI agents over JMAP: read, search, reply, organize, send.

How do I install Lettio MCP?

It runs as a remote server. In Claude Code: claude mcp add --transport http lettio-mcp 'https://mcp.lettio.eu/mcp'. For other clients, paste the JSON configuration from this page into their MCP settings.

Does Lettio MCP need an API key?

Yes. It expects LETTIO_USERNAME, LETTIO_PASSWORD, which you set in its configuration.

Is Lettio MCP open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains Lettio MCP?

It is published by lettio-eu. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.