IMAP Quota Status

A Thunderbird extension that displays IMAP mailbox quota usage as a color-coded pill in the window and as progress bars beneath each IMAP account in the folder pane.

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Features

• Status pill — floating indicator centred at the bottom of the Thunderbird window, showing the account with the highest quota usage
• Folder pane bars — thin color-coded progress bars injected beneath each IMAP account row
• Four-color scale — 🟢 green / 🔵 blue / 🟡 yellow / 🔴 red with configurable thresholds
• Tooltip — hover the pill to see all accounts with their usage
• Click to refresh — click the pill for an immediate quota update
• Configurable — poll interval, bar height, color thresholds, and visibility toggles via a settings page

Screenshots

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Requirements

• Thunderbird 128 or later
• IMAP accounts whose server supports the QUOTA capability (RFC 2087)

Permission prompt: Because this extension uses a Thunderbird Experiment API, Thunderbird will ask you to grant it "full, unrestricted access to Thunderbird and your computer" during installation. This is required for any extension that uses Experiment APIs and cannot be avoided. No about:config changes are needed — Thunderbird does not enforce extension signing by default.

Experiment API setting: This extension requires extensions.experiments.enabled to be set to true in Thunderbird. This is the default, but if the extension fails to load, verify via Edit → Preferences → General → Config Editor (or about:config) and search for extensions.experiments.enabled.

Note: Servers that do not advertise the QUOTA capability (e.g. Outlook, Hotmail, AOL) will show no quota data for those accounts.

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Installation

From the .xpi file

1. Download the latest thunderbird-imap-quota.xpi from the Releases page
2. In Thunderbird, open Tools → Add-ons and Themes
3. Click the gear icon ⚙️ and choose Install Add-on From File…
4. Select the downloaded .xpi file

From source

git clone https://github.com/elnarte/thunderbird-imap-quota.git
cd thunderbird-imap-quota
zip -r thunderbird-imap-quota.xpi . -x "*.git*" "*.DS_Store" "README.md" "LICENSE" "docs/*" "images/*"

Then install the generated .xpi as described above.

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Settings

Open Add-ons and Themes → IMAP Quota Status → Preferences to configure:

Setting	Default	Description
Show status pill	on	Show/hide the floating pill
Show folder pane bars	on	Show/hide the progress bars
Poll interval	5 min	How often quota is refreshed automatically
Bar height	4 px	Height of the folder pane progress bars
Red threshold	90%	Usage percentage at which the indicator turns red
Yellow threshold	80%	Usage percentage at which the indicator turns yellow
Blue threshold	70%	Usage percentage at which the indicator turns blue

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File Structure

thunderbird-imap-quota/
├── manifest.json          # Extension manifest (Manifest V3)
├── background.js          # Background script — orchestration and polling
├── imapQuota-api.js       # Thunderbird Experiment API — privileged XPCOM access
├── imapQuota-schema.json  # Schema declaring the experiment's public API surface
├── options.html           # Settings page UI
├── options.js             # Settings page logic
├── icons/
│   └── icon.svg           # Extension icon (SVG, scales to any resolution)
├── images/
│   ├── IMAP-Quota-Bar.jpg # Screenshot — folder pane quota bars
│   └── IMAP-Quota-Pill.jpg# Screenshot — status pill
├── docs/
│   └── technical.md       # Technical implementation documentation
└── README.md

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Technical Overview

The extension uses a Thunderbird Experiment API to access IMAP internals and inject UI elements that are unavailable to standard WebExtensions. The background script orchestrates periodic polling via messenger.alarms, reads quota data through the experiment's nsIMsgImapMailFolder.getQuota() bridge, and updates both the pill and the folder pane bars.

See docs/technical.md for a full description of the architecture, quota fetching flow, pill-click refresh mechanism, and UI injection approach.

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Compatibility

Server	QUOTA support
cPanel / Dovecot	✅ Yes
Cyrus IMAP	✅ Yes
Gmail	✅ Yes
Outlook / Hotmail	❌ No
AOL / Netscape	❌ No
Zoho Mail	❌ No
Skynet (Proximus)	✅ Yes

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Development

The extension requires no build step. Edit the source files directly and reload via about:debugging → This Thunderbird → Reload.

To inspect logs, open the extension console: about:debugging → This Thunderbird → IMAP Quota Status → Inspect.

All refresh events and quota values are logged with the [imap-quota] prefix.

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License

MIT — see LICENSE for details.

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Author

Arie Tegenbosch a.k.a. El Narte Mail

Extension implemented with Claude Sonnet 4.6 (Anthropic).