POP3 to Gmail Forwarder

A Docker-based solution that automatically fetches emails from POP3 mailboxes and forwards them to Gmail, replacing Google's discontinued POP3 import feature.

Features

• Multiple POP3 Accounts — support for unlimited POP3 mailboxes
• Dual Delivery — inject emails via Gmail API (preferred) or forward via SMTP
• Hybrid Configuration — configure via environment variables, .env files, or the database
• Smart Throttling — configurable rate limiting to stay within Gmail quotas
• Error Reporting — multi-channel notifications (Apprise: email, Telegram, Slack, Discord, webhooks)
• Scheduled Polling — configurable check intervals (default: every 5 minutes)
• Docker Ready — fully containerized with Docker Compose support
• Secure — runs as non-root user, SSL/TLS connections, encrypted credential storage

SaaS Platform (in development)

The repository also includes a multi-tenant SaaS backend built with FastAPI, PostgreSQL, Redis, and Celery. It adds multi-user support, OAuth2 authentication, POP3/IMAP protocol support, encrypted credential storage, and background job processing. See the SaaS README for details.

Quick Start

Using a Pre-built Docker Image (Recommended)

# Pull and configure
curl -O https://raw.githubusercontent.com/christianlouis/pop_puller_to_gmail/main/docker-compose.yml
curl -o .env https://raw.githubusercontent.com/christianlouis/pop_puller_to_gmail/main/.env.example

# Edit .env with your credentials
nano .env

# Start
docker-compose up -d

Building from Source

git clone https://github.com/christianlouis/pop_puller_to_gmail.git
cd pop_puller_to_gmail
cp .env.example .env   # then edit .env
docker-compose up -d

See the Quick Start Guide for detailed instructions.

Configuration

Hybrid Configuration (Environment + Database)

The application supports a hybrid configuration model:

Source	Priority	Use For
Database (app_settings table)	Highest	SMTP, processing, Gmail API, notifications
Environment variables / .env	Fallback	All settings; required for bootstrap settings
Built-in defaults	Lowest	Sensible defaults for all non-bootstrap settings

Bootstrap settings (DATABASE_URL, SECRET_KEY, ENCRYPTION_KEY) always come from environment variables because the database connection depends on them.

All other settings (SMTP, processing intervals, Gmail API, etc.) can be managed via the admin API at /api/v1/settings and are stored in the PostgreSQL database. When a database setting exists, it takes priority over the corresponding environment variable.

POP3 Accounts

Add multiple POP3 accounts by incrementing the account number in your .env:

POP3_ACCOUNT_1_HOST=pop.provider1.com
POP3_ACCOUNT_1_USER=user1@provider1.com
POP3_ACCOUNT_1_PASSWORD=password1

POP3_ACCOUNT_2_HOST=pop.provider2.com
POP3_ACCOUNT_2_USER=user2@provider2.com
POP3_ACCOUNT_2_PASSWORD=password2

Email Delivery Methods

The forwarder supports two delivery methods for getting emails into Gmail:

Gmail API Injection (Preferred)

Emails are injected directly into your Gmail account using Google's users.messages.insert() API. This is the recommended method because it:

• Preserves original email headers and metadata exactly as-is
• Does not modify From, Reply-To, or Message-ID headers
• Applies Gmail labels (e.g., INBOX) on injection
• Does not count against Gmail's SMTP sending quotas
• Does not require an SMTP App Password

Setup:

1. Configure Google OAuth2 credentials (GOOGLE_CLIENT_ID, GOOGLE_CLIENT_SECRET)
2. Authenticate via the SaaS web UI or API (POST /api/v1/providers/gmail-credential)
3. Set delivery_method to gmail_api when creating mail accounts

Required OAuth2 Scopes:

• https://www.googleapis.com/auth/gmail.insert
• https://www.googleapis.com/auth/gmail.labels

SMTP Forwarding (Fallback)

Emails are forwarded to Gmail via SMTP. This is the legacy method and is used as a fallback when Gmail API credentials are not available.

Limitations vs Gmail API:

• Modifies email headers (adds Received, may rewrite From)
• Counts against Gmail's SMTP sending quota (500/day for free accounts)
• Requires a Gmail App Password (see below)
• May trigger spam filters for forwarded mail

Setup:

1. Go to your Google Account Security
2. Under "Signing in to Google," select App Passwords
3. Generate a new app password for "Mail"
4. Set SMTP_PASSWORD in your environment or database settings

Environment Variables

Note: All settings marked ★ can also be managed via the database through the admin API (/api/v1/settings). Database values take precedence.

Bootstrap Settings (env only)

Variable	Required	Default	Description
DATABASE_URL	Yes	postgresql+asyncpg://...	PostgreSQL connection string
SECRET_KEY	Yes	—	JWT signing key (min 32 chars)
ENCRYPTION_KEY	Yes	—	Credential encryption key (min 32 chars)

POP3/IMAP Accounts (env only — or via API)

Variable	Required	Default	Description
POP3_ACCOUNT_N_HOST	Yes	—	POP3 server hostname
POP3_ACCOUNT_N_PORT	No	995	POP3 server port
POP3_ACCOUNT_N_USER	Yes	—	POP3 username
POP3_ACCOUNT_N_PASSWORD	Yes	—	POP3 password
POP3_ACCOUNT_N_USE_SSL	No	true	Use SSL/TLS

SMTP Settings (★ database-configurable)

Variable	Required	Default	Description
SMTP_HOST	No	smtp.gmail.com	SMTP server
SMTP_PORT	No	587	SMTP port
SMTP_USER	For SMTP	—	SMTP username
SMTP_PASSWORD	For SMTP	—	SMTP password (App Password)
SMTP_USE_TLS	No	true	Use STARTTLS

Gmail API Settings (★ database-configurable)

Variable	Required	Default	Description
GOOGLE_CLIENT_ID	For Gmail API	—	Google OAuth2 client ID
GOOGLE_CLIENT_SECRET	For Gmail API	—	Google OAuth2 client secret
GMAIL_API_ENABLED	No	true	Enable Gmail API delivery

Processing Settings (★ database-configurable)

Variable	Required	Default	Description
CHECK_INTERVAL_MINUTES	No	5	Polling interval
MAX_EMAILS_PER_RUN	No	50	Max emails per account per run
THROTTLE_EMAILS_PER_MINUTE	No	10	Rate limit
LOG_LEVEL	No	INFO	Logging level

How It Works

┌─────────────────┐
│  POP3 Server 1  │
└────────┬────────┘
         │ (Fetch emails)
         ▼
┌─────────────────┐      ┌──────────────────┐      ┌──────────────────┐
│  POP3 Server 2  │─────▶│    Forwarder     │─────▶│  Gmail API       │
└─────────────────┘      │    Container     │      │  (Preferred)     │
         │               │                  │      └──────────────────┘
┌────────▼────────┐      │  Config from:    │      ┌──────────────────┐
│  POP3 Server N  │      │  • Database      │─────▶│  Gmail SMTP      │
└─────────────────┘      │  • Environment   │      │  (Fallback)      │
                         └──────┬───────────┘      └──────────────────┘
                                │ (Notifications)
                                ▼
                      ┌─────────────────┐
                      │  Apprise        │
                      │  (Email, Slack, │
                      │   Telegram ...) │
                      └─────────────────┘

1. Polling — checks POP3/IMAP mailboxes at the configured interval
2. Fetching — retrieves new emails from each account
3. Delivery — injects into Gmail via API (preferred) or forwards via SMTP (fallback)
4. Cleanup — deletes from source after successful delivery
5. Throttling — respects rate limits to avoid quota issues
6. Notifications — sends alerts via Apprise (email, Telegram, Slack, Discord, webhooks)

Development

# Install dependencies
make install-dev

# Run linting & formatting
make lint
make format

# Run tests
make test

# Start backend in dev mode
make run-dev

See the Testing Guide for the full test workflow.

Documentation

Detailed documentation lives in the docs/ directory:

Document	Description
Architecture	System design and component overview
Quick Start	Step-by-step setup guide
Migration Guide	Upgrading from v1 to v2
Deployment Checklist	Production deployment guide
Roadmap	Planned features and milestones
Testing Guide	How to run and write tests
Coding Patterns	Code style and conventions
SaaS README	Multi-tenant SaaS platform details

Contributing

Contributions are welcome! Please read CONTRIBUTING.md for guidelines on:

• Reporting bugs and suggesting features
• Development setup and code style
• Pull request process

Security

To report a vulnerability, please see SECURITY.md. Do not open public issues for security concerns.

License

This project is licensed under the MIT License — see LICENSE for details.

Support

• Issue Tracker
• Discussions