Thunderbird review — open-source email client for desktop
Thunderbird is Mozilla's open-source email client. Built-in PGP encryption, multi-account support and Proton Bridge compatibility. Free alternative to Outlook.
Thunderbird review
Thunderbird is Mozilla’s open-source email client for Windows, macOS and Linux. After years of stagnation, Mozilla released a major revision in 2023 — new interface, better performance and active maintenance. The privacy-friendly choice for anyone who wants to manage email on the desktop.
Why an email client?
Webmail (Gmail in the browser, Outlook.com) processes your email on the provider’s server. An email client fetches messages to your own device via IMAP or POP3. Advantages:
- Offline access: Messages available without internet connection
- No browser tracking: Google Analytics and advertising scripts don’t run alongside
- PGP encryption: Thunderbird supports OpenPGP built-in — no extension needed
- Multiple accounts: Gmail, Proton Mail (via Bridge), work IMAP — all in one interface
Specifications
| Property | Value |
|---|---|
| Platform | Windows, macOS, Linux |
| Protocol | IMAP, POP3, SMTP |
| Encryption | OpenPGP built-in (no Enigmail needed) |
| Calendar | Built-in (Lightning) |
| Open-source | Yes (Mozilla Public License) |
| Maintained by | MZLA Technologies (Mozilla subsidiary) |
| Price | Free |
OpenPGP built-in
Thunderbird has OpenPGP key management built in. You can:
- Create a new PGP key pair directly in Thunderbird
- Import existing keys (from Kleopatra, GPG Keychain, etc.)
- Sign and encrypt emails to recipients who have shared a public key
- Import keys from key servers (keys.openpgp.org, etc.)
No extension required — works out of the box.
Proton Mail via Bridge
Proton Mail uses its own encrypted protocol that is not standard IMAP. Proton Bridge translates that to local IMAP/SMTP so Thunderbird can work with it. Setup:
- Install Proton Bridge (desktop app from Proton)
- Log in with your Proton account in Bridge
- Bridge provides a local IMAP address and password
- Add that in Thunderbird as a new account
All encryption happens in Bridge — Thunderbird sees plain IMAP. Your messages remain encrypted at Proton.
Calendar and tasks
Thunderbird has a built-in calendar (formerly Lightning extension, now standard component). Supports CalDAV — you can synchronise a Proton Calendar, Nextcloud or other CalDAV calendar.
Comparison with alternatives
| Thunderbird | Outlook | Apple Mail | Evolution | |
|---|---|---|---|---|
| Open-source | ✅ | ❌ | ❌ | ✅ |
| PGP built-in | ✅ | Via extension | Via plugin | ✅ |
| Proton Bridge | ✅ | ✅ | ✅ | ✅ |
| Calendar built-in | ✅ | ✅ | ✅ | ✅ |
| Platform | Win/Mac/Linux | Win/Mac | Mac/iOS | Linux |
| Price | Free | Microsoft 365 | Free | Free |
Caveats
Interface learning curve: Thunderbird is functional but less polished than Outlook or Apple Mail. The new Supernova interface (2023) is an improvement, but it is still a no-frills tool.
Mobile: Thunderbird has no official mobile app. On Android, K-9 Mail (now merged with Thunderbird) is the recommended choice.
Proton Bridge required: For Proton Mail, Bridge must be running — one extra background process. Not a problem, but something to account for on low-spec hardware.
Conclusion
Thunderbird is the default choice for privacy-conscious users who want to manage email on the desktop with open-source software and built-in PGP support. Combined with Proton Bridge it is the most complete privacy-friendly desktop email solution.
See also:
- Proton Mail review — encrypted email provider
- PGP practical guide — setting up PGP in Thunderbird
- Secure laptop guide — Thunderbird as part of a secure desktop environment