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

Tool	What it does
list_accounts	List the mailboxes this server is configured for.
list_mailboxes	List folders in an account, with message and unread counts.
list_recent_emails	Most recent messages in a mailbox (defaults to the inbox).
search_emails	Free‑text search across sender, subject and body.
read_email	Full content of one message by id.
send_email	Send a plain‑text email as the signed‑in mailbox.
reply_email	Reply in‑thread (keeps the conversation), optionally reply‑all.
set_read_status	Mark a message read or unread.
flag_email	Flag (star) or unflag a message.
move_email	Move 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

Variable	Required	Description
LETTIO_USERNAME	yes	Full email address, e.g. you@yourcompany.eu.
LETTIO_PASSWORD	yes	Mailbox app password.
LETTIO_HOST	no	Mail host. Defaults to https://mail.lettio.eu.
LETTIO_ACCOUNT_NAME	no	Friendly 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.