A mock Gmail MCP (Model Context Protocol) server for testing and RL environment training. It simulates a complete email system without requiring any network connectivity - all state is loaded from and persisted to a JSON file.

Overview

This MCP server provides 20 email tools that operate on a "closed-world" simulation:

Closed-world contacts: Only predefined email addresses can receive messages
Bounce simulation: Emails to invalid addresses generate realistic bounce notifications
Group support: Sending to a group delivers copies to members (including yourself if you're a member)
State persistence: All changes are saved back to the JSON file
No network required: Everything runs locally from a JSON file

Project Structure

packages/google_mail/
├── google_mail.py      # Entry point for container environment
├── utils.py            # Utilities for data path computation
├── __init__.py         # Package exports
├── src/mail_mcp/       # Core MCP server implementation
│   ├── server.py       # FastMCP server with tool definitions
│   ├── models/         # Pydantic schemas
│   └── services/       # Mailbox business logic
├── examples/
│   └── sample_mailbox.json
└── tests/

Installation

Local Development

cd packages/google_mail
uv sync

Container Environment

The MCP server is pre-installed in the DAT container. Data is stored in external_services/mailbox.json next to the agent workspace (outside the agent's filesystem access).

Usage

Running Locally

# Using environment variable
MAIL_MCP_DATA_PATH=/path/to/mailbox.json uv run mail-mcp

# Using CLI argument
uv run mail-mcp --data-path /path/to/mailbox.json

# With debug logging
uv run mail-mcp --data-path /path/to/mailbox.json --debug

Container Usage (via MCP Config)

The server is configured in configs/mcp_servers/google_mail.yaml:

type: stdio
name: google_mail
params:
  command: uv
  args:
    - "run"
    - "--project"
    - "/workspace/packages/google_mail"
    - "python"
    - "/workspace/packages/google_mail/google_mail.py"
    - "--agent-workspace"
    - "${agent_workspace}"

Task Preprocessing

To set up mailbox data for a task, use the utility functions:

from google_mail import create_mail_data
from pathlib import Path

# Copy mailbox.json to external_services location
create_mail_data(
    agent_workspace="/workspace/dumps/workspace",
    source_mailbox_path=Path("initial_workspace/mailbox.json"),
)

MCP Client Configuration

For direct MCP client usage:

{
  "mcpServers": {
    "mail": {
      "command": "uv",
      "args": ["run", "--project", "/path/to/google_mail", "mail-mcp"],
      "env": {
        "MAIL_MCP_DATA_PATH": "/path/to/mailbox.json"
      }
    }
  }
}

Tools

Email Operations

Tool	Description
`mail_get_emails`	Get paginated emails from a folder
`mail_read_email`	Read a single email (marks as read)
`mail_search_emails`	Search emails by query string, including Gmail-style operators such as `from:`, `subject:`, `has:attachment`, `filename:`, `is:unread`, and `in:`
`mail_send_email`	Send an email
`mail_reply_email`	Reply to an email
`mail_forward_email`	Forward an email with attachments
`mail_delete_emails`	Delete one or more emails (moves to Trash or permanent)
`mail_move_emails`	Move one or more emails to a different folder
`mail_mark_emails`	Mark emails as read/unread/important

Folder Operations

Tool	Description
`mail_get_folders`	List all folders with message counts
`mail_create_folder`	Create a new folder
`mail_delete_folder`	Delete a folder (system folders protected)
`mail_get_unread_count`	Get unread counts per folder
`mail_get_mailbox_stats`	Get statistics for all folders

Draft Operations

Tool	Description
`mail_save_draft`	Save a new draft
`mail_get_drafts`	Get paginated list of drafts
`mail_update_draft`	Update an existing draft
`mail_delete_draft`	Delete a draft

Other

Tool	Description
`mail_get_contacts`	List all valid contacts (closed-world)
`mail_download_attachment`	Download an attachment as base64

Threading

Emails are linked into threads via the in_reply_to field, which references the parent email's message_id.

When using mail_reply_email:

The reply's in_reply_to is automatically set to the original's message_id
The reply body includes a quoted copy of the original message:

Your reply here...

--- Original Message ---
From: alice@example.com
Date: 2024-01-15 10:30
Subject: Meeting Tomorrow

Original message content...

This provides both programmatic thread linking (via in_reply_to) and human-readable context (via quoted original).

JSON Schema

The mailbox data file follows this schema:

Root Structure

{
  "mailbox": { ... },
  "contacts": [ ... ],
  "folders": [ ... ],
  "emails": [ ... ],
  "drafts": [ ... ],
  "next_email_id": 1
}

Fields

mailbox (required)

The identity of the mailbox owner. This is the "From" address when sending emails.

{
  "email": "user@example.com",
  "name": "Display Name"
}

contacts (required)

List of valid email recipients. Only these addresses (plus the mailbox owner) can receive emails. Sending to any other address will generate a bounce notification.

[
  {"email": "alice@example.com", "name": "Alice Smith"},
  {"email": "team@example.com", "name": "Engineering Team", "members": [
    "user@example.com",
    "alice@example.com"
  ]}
]

Groups have a members array. When you send to a group and you're a member, you receive a copy in your INBOX.

folders (optional)

Custom folders beyond the system defaults. System folders (INBOX, Sent, Drafts, Trash) always exist implicitly.

[
  {"name": "Work"},
  {"name": "Archive/2024"}
]

emails (optional)

List of emails in the mailbox.

[
  {
    "email_id": "1",
    "folder": "INBOX",
    "subject": "Meeting Tomorrow",
    "from_addr": "alice@example.com",
    "to_addr": "user@example.com",
    "cc_addr": null,
    "bcc_addr": null,
    "date": "2024-01-15T10:30:00Z",
    "message_id": "<msg001@example.com>",
    "in_reply_to": null,
    "body_text": "Plain text content here",
    "body_html": "<p>Optional HTML content</p>",
    "is_read": false,
    "is_important": false,
    "attachments": [
      {
        "filename": "document.pdf",
        "content_type": "application/pdf",
        "content_base64": "JVBERi0xLjQK..."
      }
    ]
  }
]

The in_reply_to field links replies to their parent email via message_id. This enables thread tracking.

drafts (optional)

List of draft emails.

[
  {
    "draft_id": "draft_1",
    "subject": "Draft Subject",
    "body": "Draft content",
    "html_body": null,
    "to": "alice@example.com",
    "cc": null,
    "bcc": null,
    "created_at": "2024-01-15T09:00:00Z",
    "updated_at": "2024-01-15T09:30:00Z"
  }
]

next_email_id (optional)

Counter for generating new email IDs. Defaults to 1 if not specified.

Examples

Minimal Empty Mailbox

{
  "mailbox": {
    "email": "user@example.com",
    "name": "Test User"
  },
  "contacts": [],
  "folders": [],
  "emails": [],
  "drafts": [],
  "next_email_id": 1
}

Populated Mailbox

See examples/sample_mailbox.json for a complete example with contacts, emails, groups, drafts, and attachments.

Development

Running Tests

cd packages/google_mail
uv run pytest

Code Quality

uv run ruff check .
uv run mypy .