MCP Gmail & PostgreSQL Server

A unified Model Context Protocol (MCP) server that provides AI agents with read and write access to Gmail and PostgreSQL databases.

🚀 Two Modes Available

1. stdio Mode (for Claude Desktop)

• Direct integration with Claude Desktop
• Uses standard input/output
• No network configuration needed

2. HTTP/SSE Mode (for n8n, remote agents)

• HTTP server with Server-Sent Events (SSE)
• Can be deployed to VPS
• Accessible via URL
• Perfect for n8n AI Agent with MCP Client connector

Features

• Gmail Integration: Send emails, read emails, list emails, and manage labels
• PostgreSQL Integration: Execute queries, read/write operations, and schema inspection
• Modular Architecture: Cleanly separated services for easy maintenance
• Environment-based Configuration: Secure credential management via .env file

Prerequisites

• Node.js 18+
• npm or yarn
• Gmail API credentials (Google Cloud Console)
• PostgreSQL database

Installation

1. Clone and install dependencies:

npm install

2. Build the project:

npm run build

Configuration

Step 1: Create .env file

Copy the example file and fill in your credentials:

cp .env.example .env

Step 2: Configure Gmail

Get Gmail API Credentials

1. Go to Google Cloud Console

2. Create a new project or select an existing one

3. Enable the Gmail API:

   • Navigate to "APIs & Services" > "Library"
   • Search for "Gmail API" and click "Enable"

4. Create OAuth 2.0 credentials:

   • Go to "APIs & Services" > "Credentials"
   • Click "Create Credentials" > "OAuth client ID"
   • Choose "Desktop app" as application type
   • Download the credentials JSON file

5. Get your Client ID and Client Secret from the credentials

6. Get a Refresh Token:

   • Run this script to authorize and get a refresh token:

   node scripts/get-gmail-token.js
   

   • Or use Google's OAuth 2.0 Playground:
     1. Go to https://developers.google.com/oauthplayground/
     2. Click the gear icon (⚙️) and check "Use your own OAuth credentials"
     3. Enter your Client ID and Client Secret
     4. In the left panel, select "Gmail API v1" and check the scopes:
        • https://www.googleapis.com/auth/gmail.readonly
        • https://www.googleapis.com/auth/gmail.send
        • https://www.googleapis.com/auth/gmail.modify
     5. Click "Authorize APIs" and sign in
     6. Click "Exchange authorization code for tokens"
     7. Copy the "Refresh token" value

7. Add to .env:

GMAIL_CLIENT_ID=your_client_id_from_step_5
GMAIL_CLIENT_SECRET=your_client_secret_from_step_5
GMAIL_REFRESH_TOKEN=your_refresh_token_from_step_6

Step 3: Configure PostgreSQL

Add your PostgreSQL connection details to .env:

POSTGRES_HOST=localhost          # or your database host
POSTGRES_PORT=5432               # default PostgreSQL port
POSTGRES_DATABASE=your_db_name   # your database name
POSTGRES_USER=your_db_user       # your database user
POSTGRES_PASSWORD=your_password  # your database password
POSTGRES_SSL=false               # set to true if using SSL

Usage

For n8n (HTTP Mode) - RECOMMENDED

Start the HTTP server:

# Development
npm run dev:http

# Production
npm run build
npm run start:http

Server will be available at: http://localhost:3000/sse

See N8N_SETUP.md for complete n8n integration guide.

For Claude Desktop (stdio Mode)

# Development
npm run dev

# Production
npm start

Configure in Claude Desktop's config file (see Configuration section below).

Available Tools

Gmail Tools

• gmail_list_emails: List emails from inbox with optional filters
  • Parameters: query, maxResults, labelIds
• gmail_read_email: Read a specific email by message ID
  • Parameters: messageId, format
• gmail_send_email: Send an email
  • Parameters: to, subject, body, htmlBody (optional), cc (optional), bcc (optional)
• gmail_get_labels: Get all Gmail labels

PostgreSQL Tools

• postgres_query: Execute SELECT queries (read-only)
  • Parameters: query, params (optional array)
• postgres_execute: Execute write operations (INSERT, UPDATE, DELETE)
  • Parameters: query, params (optional array)
• postgres_get_tables: List all tables in the database
  • Parameters: schema (optional, default: 'public')
• postgres_get_table_schema: Get schema information for a table
  • Parameters: tableName, schema (optional, default: 'public')

Deployment to VPS

1. Transfer files to your VPS:

scp -r . user@your-vps-ip:/path/to/mcp-server/

2. SSH into your VPS and install:

ssh user@your-vps-ip
cd /path/to/mcp-server
npm install
npm run build

3. Create .env file on VPS with your credentials

4. Run as a service (using PM2 or systemd):

With PM2:

npm install -g pm2
pm2 start npm --name "mcp-server" -- start
pm2 save

With systemd, create /etc/systemd/system/mcp-server.service:

[Unit]
Description=MCP Gmail & PostgreSQL Server
After=network.target

[Service]
Type=simple
User=your-user
WorkingDirectory=/path/to/mcp-server
Environment=NODE_ENV=production
ExecStart=/usr/bin/node dist/index.js
Restart=always

[Install]
WantedBy=multi-user.target

Then:

sudo systemctl enable mcp-server
sudo systemctl start mcp-server

Project Structure

.
├── src/
│   ├── index.ts              # Main server entry point
│   └── services/
│       ├── gmail.service.ts  # Gmail integration
│       └── postgres.service.ts # PostgreSQL integration
├── dist/                     # Compiled JavaScript
├── .env                      # Environment variables (not in git)
├── .env.example             # Example environment file
├── package.json
├── tsconfig.json
└── README.md

Security Notes

• Never commit .env file to version control
• Use strong database passwords
• Keep Gmail OAuth credentials secure
• Consider using environment-specific credentials for production
• Regularly rotate refresh tokens and passwords

Troubleshooting

Gmail not working

• Verify your refresh token is valid and not expired
• Check that all required OAuth scopes are granted
• Ensure GMAIL_CLIENT_ID and GMAIL_CLIENT_SECRET are correct

PostgreSQL connection issues

• Verify database credentials are correct
• Check if PostgreSQL is running and accessible
• For remote connections, ensure firewall rules allow connections
• If using SSL, set POSTGRES_SSL=true in .env

License

MIT