mail2couch

A powerful email backup utility that synchronizes mail from IMAP accounts to CouchDB databases with intelligent incremental sync, comprehensive filtering, and native attachment support.

Features

Core Functionality

• IMAP Email Backup: Connect to any IMAP server (Gmail, Outlook, self-hosted)
• CouchDB Storage: Store emails as JSON documents with native CouchDB attachments
• Incremental Sync: Efficiently sync only new messages using IMAP SEARCH with timestamp tracking
• Per-Account Databases: Each mail source gets its own CouchDB database for better organization
• Duplicate Prevention: Automatic detection and prevention of duplicate message storage

Sync Modes

• Archive Mode: Preserve all messages ever seen, even if deleted from mail server (default)
• Sync Mode: Maintain 1-to-1 relationship with mail server (removes deleted messages from CouchDB)

Advanced Filtering

• Wildcard Folder Patterns: Use *, ?, [abc] patterns for flexible folder selection
• Keyword Filtering: Filter messages by keywords in subjects, senders, or recipients
• Date Filtering: Process only messages since a specific date
• Include/Exclude Logic: Combine multiple filter types for precise control

Message Processing

• Full MIME Support: Parse multipart messages, HTML/plain text, and embedded content
• Native Attachments: Store email attachments as CouchDB native attachments with compression
• Complete Headers: Preserve all email headers and metadata
• UTF-8 Support: Handle international characters and special content

Operational Features

• Automatic Config Discovery: Finds configuration files in standard locations
• Command Line Control: Override settings with --max-messages and --config flags
• Comprehensive Logging: Detailed output for monitoring and troubleshooting
• Error Resilience: Graceful handling of network issues and server problems

Quick Start

Installation

1. Install dependencies:

   # Go 1.21+ required
   go version
   

2. Clone and build:

   git clone <repository-url>
   cd mail2couch/go
   go build -o mail2couch .
   

Basic Usage

1. Create configuration file (config.json):

   {
     "couchDb": {
       "url": "http://localhost:5984",
       "user": "admin", 
       "password": "password"
     },
     "mailSources": [
       {
         "name": "Personal Gmail",
         "enabled": true,
         "protocol": "imap",
         "host": "imap.gmail.com",
         "port": 993,
         "user": "your-email@gmail.com",
         "password": "your-app-password",
         "mode": "archive",
         "folderFilter": {
           "include": ["*"],
           "exclude": ["[Gmail]/Trash", "[Gmail]/Spam"]
         }
       }
     ]
   }
   

2. Run mail2couch:

   ./mail2couch
   

The application will:

• Create a CouchDB database named m2c_personal_gmail
• Sync all folders except Trash and Spam
• Store messages with native attachments
• Track sync state for efficient incremental updates

Configuration

Configuration File Discovery

mail2couch automatically searches for configuration files in this order:

1. Path specified by --config flag
2. ./config.json (current directory)
3. ./config/config.json (config subdirectory)
4. ~/.config/mail2couch/config.json (user config directory)
5. ~/.mail2couch.json (user home directory)

Command Line Options

./mail2couch [options]

Options:
  --config PATH        Specify configuration file path
  --max-messages N     Limit messages processed per mailbox per run (0 = unlimited)

Folder Pattern Examples

Pattern	Description	Matches
"*"	All folders	INBOX, Sent, Work/Projects, etc.
"INBOX"	Exact match	INBOX only
"Work*"	Prefix match	Work, Work/Projects, WorkStuff
"*/Archive"	Suffix match	Personal/Archive, Work/Archive
"Work/*"	Subfolder match	Work/Projects, Work/Clients

Keyword Filtering Examples

{
  "messageFilter": {
    "subjectKeywords": ["urgent", "meeting", "invoice"],
    "senderKeywords": ["@company.com", "noreply@"],
    "recipientKeywords": ["team@", "support@"]
  }
}

Advanced Configuration Examples

See the example configurations section below for detailed configuration scenarios.

Testing

A comprehensive test environment is included with Podman containers:

cd test

# Quick automated testing (recommended)
./run-tests.sh              # Complete integration test with automatic cleanup

# Specialized feature testing  
./test-wildcard-patterns.sh # Test folder pattern matching
./test-incremental-sync.sh  # Test incremental synchronization

# Manual testing environment
./start-test-env.sh         # Start persistent test environment
# ... manual testing with various configurations ...
./stop-test-env.sh          # Clean up when done

Architecture

Database Structure

• Per-Account Databases: Each mail source creates its own CouchDB database with m2c_ prefix
• Message Documents: Each email becomes a CouchDB document with metadata
• Native Attachments: Email attachments stored as CouchDB attachments (compressed)
• Sync Metadata: Tracks incremental sync state per mailbox

Document Structure

{
  "_id": "INBOX_12345",
  "sourceUid": "12345", 
  "mailbox": "INBOX",
  "from": ["sender@example.com"],
  "to": ["recipient@example.com"],
  "subject": "Sample Email",
  "date": "2024-01-15T10:30:00Z",
  "body": "Email content...",
  "headers": {"Content-Type": ["text/plain"]},
  "storedAt": "2024-01-15T10:35:00Z",
  "docType": "mail",
  "hasAttachments": true,
  "_attachments": {
    "document.pdf": {
      "content_type": "application/pdf",
      "length": 54321
    }
  }
}

Example Configurations

Simple Configuration

Basic setup for a single Gmail account:

{
  "couchDb": {
    "url": "http://localhost:5984",
    "user": "admin",
    "password": "password"
  },
  "mailSources": [
    {
      "name": "Personal Gmail",
      "enabled": true,
      "protocol": "imap",
      "host": "imap.gmail.com", 
      "port": 993,
      "user": "your-email@gmail.com",
      "password": "your-app-password",
      "mode": "archive",
      "folderFilter": {
        "include": ["INBOX", "Sent"],
        "exclude": []
      },
      "messageFilter": {
        "since": "2024-01-01"
      }
    }
  ]
}

Advanced Multi-Account Configuration

Complex setup with multiple accounts, filtering, and different sync modes:

{
  "couchDb": {
    "url": "https://your-couchdb.example.com:5984",
    "user": "backup_user",
    "password": "secure_password"
  },
  "mailSources": [
    {
      "name": "Work Email", 
      "enabled": true,
      "protocol": "imap",
      "host": "outlook.office365.com",
      "port": 993,
      "user": "you@company.com",
      "password": "app-password",
      "mode": "sync",
      "folderFilter": {
        "include": ["*"],
        "exclude": ["Deleted Items", "Junk Email", "Drafts"]
      },
      "messageFilter": {
        "since": "2023-01-01",
        "subjectKeywords": ["project", "meeting", "urgent"],
        "senderKeywords": ["@company.com", "@client.com"]
      }
    },
    {
      "name": "Personal Gmail",
      "enabled": true, 
      "protocol": "imap",
      "host": "imap.gmail.com",
      "port": 993,
      "user": "personal@gmail.com",
      "password": "gmail-app-password",
      "mode": "archive",
      "folderFilter": {
        "include": ["INBOX", "Important", "Work/*", "Personal/*"],
        "exclude": ["[Gmail]/Trash", "[Gmail]/Spam", "*Temp*"]
      },
      "messageFilter": {
        "recipientKeywords": ["family@", "personal@"]
      }
    },
    {
      "name": "Self-Hosted Mail",
      "enabled": true,
      "protocol": "imap", 
      "host": "mail.yourdomain.com",
      "port": 143,
      "user": "admin@yourdomain.com",
      "password": "mail-password",
      "mode": "archive",
      "folderFilter": {
        "include": ["INBOX", "Archive/*", "Projects/*"],
        "exclude": ["*/Drafts", "Trash"]
      },
      "messageFilter": {
        "since": "2023-06-01",
        "subjectKeywords": ["invoice", "receipt", "statement"]
      }
    },
    {
      "name": "Legacy Account",
      "enabled": false,
      "protocol": "imap",
      "host": "legacy.mailserver.com", 
      "port": 993,
      "user": "old@account.com",
      "password": "legacy-password",
      "mode": "archive",
      "folderFilter": {
        "include": ["INBOX"],
        "exclude": []
      },
      "messageFilter": {}
    }
  ]
}

Configuration Options Reference

CouchDB Configuration

• url: CouchDB server URL with protocol and port
• user: CouchDB username with database access
• password: CouchDB password

Mail Source Configuration

• name: Descriptive name (used for database naming)
• enabled: Boolean to enable/disable this source
• protocol: Only "imap" currently supported
• host: IMAP server hostname
• port: IMAP port (993 for TLS, 143 for plain, 3143 for testing)
• user: Email account username
• password: Email account password (use app passwords for Gmail/Outlook)
• mode: "sync" (mirror server) or "archive" (preserve all messages)

Folder Filter Configuration

• include: Array of folder patterns to process (empty = all folders)
• exclude: Array of folder patterns to skip

Message Filter Configuration

• since: Date string (YYYY-MM-DD) to process messages from
• subjectKeywords: Array of keywords that must appear in subject line
• senderKeywords: Array of keywords that must appear in sender addresses
• recipientKeywords: Array of keywords that must appear in recipient addresses

Production Deployment

Security Considerations

• Use app passwords instead of account passwords
• Store configuration files with restricted permissions (600)
• Use HTTPS for CouchDB connections in production
• Consider encrypting sensitive configuration data

Monitoring and Maintenance

• Review sync metadata documents for sync health
• Monitor CouchDB database sizes and compaction
• Set up log rotation for application output
• Schedule regular backups of CouchDB databases

Performance Tuning

• Use --max-messages to limit processing load
• Run during off-peak hours for large initial syncs
• Monitor IMAP server rate limits and connection limits
• Consider running multiple instances for different accounts

Troubleshooting

Common Issues

Connection Errors:

• Verify IMAP server settings and credentials
• Check firewall and network connectivity
• Ensure correct ports (993 for TLS, 143 for plain)

Authentication Failures:

• Use app passwords for Gmail, Outlook, and other providers
• Enable "Less Secure Apps" if required by provider
• Verify account permissions and 2FA settings

Sync Issues:

• Check CouchDB connectivity and permissions
• Review sync metadata documents for error states
• Verify folder names and patterns match server structure

Performance Problems:

• Use date filtering (since) for large mailboxes
• Implement --max-messages limits for initial syncs
• Monitor server-side rate limiting

For detailed troubleshooting, see the test environment documentation.

Contributing

This project welcomes contributions! Please see CLAUDE.md for development setup and architecture details.

License

[License information to be added]