FolderSync

A Thunderbird add-on that synchronizes email messages between folders across different accounts.

Features

• Bidirectional & one-way sync — Choose between A ↔ B, A → B, or B → A synchronization
• Multiple sync configurations — Set up as many folder pairs as you need
• Automatic sync — Schedule periodic synchronization with configurable intervals (1–1440 minutes)
• Deduplication — Messages are matched by Message-ID and occurrence count. Messages without an ID use a metadata fingerprint (date, subject, sender, recipients, and size); identical fingerprints are compared by count.
• Batch processing — Large folders are handled efficiently with pagination and batch copying
• Real-time status — See sync progress, last sync time, and copied message counts
• Localization — English and German UI

Installation

From file

1. Download the latest .xpi file from the Releases page
2. In Thunderbird, go to Add-ons Manager → Extensions
3. Click the gear icon → Install Add-on From File…
4. Select the downloaded .xpi file

Build from source

git clone https://github.com/your-username/folder-sync.git
cd folder-sync
./build.sh

This creates a foldersync-<version>.xpi file ready for installation.

Usage

1. Click the FolderSync icon in the Thunderbird toolbar
2. Click Add new sync to create a sync configuration
3. Select the source and destination accounts and folders
4. Choose the sync direction
5. Optionally enable automatic sync with your preferred interval
6. Click Save, then Sync now to run the first synchronization

Requirements

• Thunderbird 128.0 or later

Permissions

Permission	Reason
accountsRead	List available email accounts
messagesRead	Read message headers for deduplication
messagesMove	Copy messages between folders
storage	Persist sync configurations
alarms	Schedule automatic synchronization

License

MIT