📧 Gmail MCP Server

Dual-mode Gmail integration: Direct CLI operations + MCP server for AI assistants

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Overview

Gmail MCP Server is a versatile .NET global tool that bridges your Gmail account with both human users and AI assistants. It provides two distinct modes of operation:

CLI Mode - Direct command-line interface for searching messages, reading emails, and downloading attachments using familiar terminal commands.

MCP Mode - Model Context Protocol server that enables AI assistants (like Claude) to interact with your Gmail account through a standardized protocol.

What Problems It Solves

• AI Email Integration: Give AI assistants secure, controlled access to your Gmail without sharing passwords
• Terminal Email Access: Quickly search and read emails from the command line for scripting and automation
• OAuth2 Security: Browser-based authentication flow with local credential storage
• Cross-Platform: Works on Windows, macOS, and Linux with .NET runtime

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✨ Features

• 🔄 Dual-mode architecture - Switch between CLI and MCP server modes seamlessly
• 🔐 OAuth2 auto-authentication - Secure browser-based authentication with automatic token refresh
• 📧 Gmail operations - Search messages with Gmail query syntax, read full email content, download attachments
• 🤖 MCP integration - Standardized protocol for AI assistants (Claude Desktop, Cline, etc.)
• 📦 Easy installation - Available as .NET global tool via NuGet
• 🔍 Advanced search - Full Gmail query syntax support (from:, subject:, is:unread, etc.)
• 💻 Script-friendly - JSON output mode for automation and integration
• 🌐 Cross-platform - Runs anywhere .NET 8.0 or 10.0 is supported

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🚀 Quick Start

# Install the global tool
dotnet tool install -g GmailMcp

# Authenticate with your Gmail account
dotnet-gmail auth

# Search for messages (CLI mode)
dotnet-gmail search "from:example@gmail.com"

# Read a specific message
dotnet-gmail read <message-id>

# Start MCP server for AI assistants
dotnet-gmail mcp

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📦 Installation

Prerequisites

• .NET 8.0 or 10.0 SDK - Download here
• Google Cloud Console account - Required for OAuth2 credentials
• Gmail account - The account you want to access

Step 1: Google Cloud Console Setup

1. Go to Google Cloud Console
2. Create a new project or select an existing one
3. Enable the Gmail API for your project
4. Navigate to Credentials > Create Credentials > OAuth 2.0 Client ID
5. Choose Desktop app as the application type
6. Download the credentials JSON file
7. Rename it to gcp-oauth.keys.json
8. Place it in ~/.gmail-mcp/ (create the directory if needed)

File location:

• Windows: %USERPROFILE%\.gmail-mcp\gcp-oauth.keys.json
• macOS/Linux: ~/.gmail-mcp/gcp-oauth.keys.json

Step 2: Install the Tool

dotnet tool install -g GmailMcp

Step 3: Authenticate

dotnet-gmail auth

This will:

1. Open your default browser
2. Prompt you to sign in to Google
3. Request permission to access your Gmail
4. Save the OAuth2 tokens locally in ~/.gmail-mcp/token.json

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🔧 Usage

CLI Mode

Authentication

# Authenticate and store credentials
dotnet-gmail auth

Search Messages

# Basic search
dotnet-gmail search "from:john@example.com"

# Search with subject
dotnet-gmail search "subject:invoice"

# Complex query
dotnet-gmail search "from:support@company.com is:unread after:2024/01/01"

# Limit results (default: 10)
dotnet-gmail search "from:boss@company.com" --max-results 5

# JSON output for scripting
dotnet-gmail search "is:unread" --robot

Common search operators:

• from:user@example.com - Emails from specific sender
• to:user@example.com - Emails to specific recipient
• subject:keyword - Subject contains keyword
• is:unread - Unread messages only
• has:attachment - Messages with attachments
• after:2024/01/01 - Messages after date
• before:2024/12/31 - Messages before date

Read Message

# Read message by ID (get ID from search results)
dotnet-gmail read 18d4f2a3b5c6e7f8

# JSON output
dotnet-gmail read 18d4f2a3b5c6e7f8 --robot

Download Attachment

# Download to current directory
dotnet-gmail download <message-id> <attachment-id>

# Download to specific directory
dotnet-gmail download <message-id> <attachment-id> --output ./downloads

# Custom filename
dotnet-gmail download <message-id> <attachment-id> --filename report.pdf

MCP Mode

Quick MCP Setup

Add the following to your Claude Desktop configuration file:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "gmail": {
      "command": "dotnet-gmail",
      "args": ["mcp"]
    }
  }
}

Restart Claude Desktop after making changes.

For detailed MCP configuration instructions, troubleshooting, and advanced setup options, see the MCP Configuration Guide.

Available MCP Tools

Once configured, Claude can use these tools:

Tool	Parameters	Description
search_messages	query, maxResults	Search Gmail using query syntax, returns message metadata
read_message	messageId	Read full message content including body and attachments
download_attachment	messageId, attachmentId, outputDirectory, filename	Download specific attachment to disk

Example Claude prompts:

• "Search my Gmail for unread messages from support@example.com"
• "Read the message with ID 18d4f2a3b5c6e7f8"
• "Download the PDF attachment from that email"
• "Find all emails from my boss in the last week with attachments"

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🏗️ Architecture

┌─────────────────────────────────────────────────┐
│              Gmail MCP Server                   │
│                                                 │
│  ┌──────────────┐         ┌─────────────────┐  │
│  │   CLI Mode   │         │   MCP Mode      │  │
│  │              │         │                 │  │
│  │  • auth      │         │  • stdio server │  │
│  │  • search    │         │  • tool calls   │  │
│  │  • read      │         │  • JSON-RPC     │  │
│  │  • download  │         │                 │  │
│  └──────┬───────┘         └────────┬────────┘  │
│         │                          │           │
│         └──────────┬───────────────┘           │
│                    │                           │
│         ┌──────────▼──────────┐                │
│         │  Shared Services    │                │
│         │                     │                │
│         │  • AuthService      │                │
│         │  • GmailService     │                │
│         └──────────┬──────────┘                │
│                    │                           │
│         ┌──────────▼──────────┐                │
│         │    Gmail API v1     │                │
│         │  (Google.Apis)      │                │
│         └─────────────────────┘                │
└─────────────────────────────────────────────────┘

Key Components:

• Program.cs - Entry point with dependency injection setup
• Commands - CLI command implementations (auth, search, read, download)
• Services - Shared business logic (authentication, Gmail operations)
• MCP Server - Model Context Protocol server and tool definitions
• Models - Data structures for messages and attachments

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🔐 Authentication & Security

OAuth2 Flow

Gmail MCP Server uses OAuth2 for secure authentication:

1. Client credentials (gcp-oauth.keys.json) stored in ~/.gmail-mcp/
2. User consent obtained through browser-based Google login
3. Access tokens stored locally in ~/.gmail-mcp/token.json
4. Automatic refresh when tokens expire

Security Best Practices

• Never commit gcp-oauth.keys.json or token.json to version control
• Restrict OAuth scopes to minimum required (currently uses GmailReadonlyScope)
• Review granted permissions in Google Account settings
• Rotate credentials if you suspect compromise

Setting Up Google Cloud Credentials

Detailed Steps:

1. Navigate to Google Cloud Console

2. Create a new project:

   • Click "Select a project" > "New Project"
   • Name it (e.g., "Gmail MCP Access")
   • Click "Create"

3. Enable Gmail API:

   • Go to "APIs & Services" > "Library"
   • Search for "Gmail API"
   • Click "Enable"

4. Create OAuth 2.0 credentials:

   • Go to "APIs & Services" > "Credentials"
   • Click "+ CREATE CREDENTIALS" > "OAuth client ID"
   • If prompted, configure the OAuth consent screen:
     • User Type: "External"
     • App name: "Gmail MCP Server"
     • User support email: your email
     • Developer contact: your email
     • Save and continue through remaining steps
   • Application type: "Desktop app"
   • Name: "Gmail MCP Desktop"
   • Click "Create"

5. Download credentials:

   • Click the download icon (⬇) next to your newly created OAuth client
   • Save as gcp-oauth.keys.json
   • Move to ~/.gmail-mcp/gcp-oauth.keys.json

6. First authentication:

   dotnet-gmail auth
   

   • Browser opens automatically
   • Sign in with your Google account
   • Grant requested permissions
   • Token saved to ~/.gmail-mcp/token.json

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🛠️ Development

Clone & Build

# Clone repository
git clone https://github.com/yourusername/dotnet-gmail-mcp.git
cd dotnet-gmail-mcp

# Build solution
dotnet build

# Run locally
dotnet run --project src/GmailMcp

Local Testing

Test CLI Commands

# Build and install locally
dotnet pack src/GmailMcp
dotnet tool install -g --add-source ./src/GmailMcp/nupkg GmailMcp

# Test authentication
dotnet-gmail auth

# Test search
dotnet-gmail search "is:unread" --max-results 5

# Test read
dotnet-gmail read <message-id>

# Uninstall when done
dotnet tool uninstall -g GmailMcp

Test MCP Integration

# Start MCP server in one terminal
dotnet-gmail mcp

# In another terminal, send MCP protocol messages via stdin
# (or configure Claude Desktop to use local build)

Project Structure

dotnet-gmail-mcp/
├── src/
│   └── GmailMcp/
│       ├── Commands/           # CLI command implementations
│       │   ├── AuthCommand.cs
│       │   ├── SearchCommand.cs
│       │   ├── ReadCommand.cs
│       │   ├── DownloadCommand.cs
│       │   └── McpCommand.cs
│       ├── Services/           # Business logic layer
│       │   ├── IAuthenticationService.cs
│       │   ├── AuthenticationService.cs
│       │   ├── IGmailService.cs
│       │   └── GmailService.cs
│       ├── Models/             # Data structures
│       │   ├── GmailMessage.cs
│       │   └── GmailAttachment.cs
│       ├── Mcp/                # MCP server and tools
│       │   ├── GmailMcpServer.cs
│       │   └── Tools/
│       │       ├── SearchMessagesTool.cs
│       │       ├── ReadMessageTool.cs
│       │       └── DownloadAttachmentTool.cs
│       ├── Program.cs          # Entry point and DI setup
│       └── GmailMcp.csproj     # Project configuration
└── README.md

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📋 MCP Tools Reference

search_messages

Search Gmail messages using Gmail query syntax.

Parameters:

• query (string, required) - Gmail search query (e.g., "from:user@example.com", "subject:meeting", "is:unread")
• maxResults (int, optional) - Maximum number of results to return (default: 10, max: 100)

Returns: JSON array of message objects with:

• id - Message ID
• threadId - Thread ID
• subject - Email subject
• from - Sender email address
• to - Array of recipient email addresses
• date - ISO 8601 formatted date
• hasAttachments - Boolean indicating if attachments exist
• attachmentCount - Number of attachments

Example:

{
  "query": "from:boss@company.com is:unread",
  "maxResults": 5
}

read_message

Read full content of a specific Gmail message.

Parameters:

• messageId (string, required) - Unique message identifier from search results

Returns: JSON object with:

• id - Message ID
• threadId - Thread ID
• subject - Email subject
• from - Sender email address
• to - Array of recipient email addresses
• date - ISO 8601 formatted date
• body - Plain text email body
• attachments - Array of attachment objects with id, filename, mimeType, size

Example:

{
  "messageId": "18d4f2a3b5c6e7f8"
}

download_attachment

Download an attachment from a Gmail message to local disk.

Parameters:

• messageId (string, required) - Message containing the attachment
• attachmentId (string, required) - Attachment identifier from message
• outputDirectory (string, optional) - Directory to save file (default: current directory)
• filename (string, optional) - Custom filename (default: original filename)

Returns: JSON object with:

• filePath - Full path to downloaded file
• filename - Name of the saved file
• size - File size in bytes

Example:

{
  "messageId": "18d4f2a3b5c6e7f8",
  "attachmentId": "ANGjdJ8wK...",
  "outputDirectory": "./downloads",
  "filename": "report.pdf"
}

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🤝 Contributing

Contributions are welcome! Please feel free to submit issues, fork the repository, and create pull requests.

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

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📄 License

This project is licensed under the MIT License. See LICENSE file for details.

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🔗 Related Projects

• Model Context Protocol - MCP specification and SDKs
• Claude Desktop - AI assistant with MCP support
• Google APIs .NET - Gmail API client library

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Built with ❤️ using .NET and Model Context Protocol