Thunderbird
A free, open source email app that combines mail, calendars and contacts, funded by donations.
Our verdict
What it does well
- Free, with the site calling it 'Free forever'
- Unified inbox, or each account managed separately
- Messages, calendars and contacts in one app
Where it falls short
- The Android app is a separate project, based on K-9 Mail
- No iOS app is listed on the download page
- No paid plans or official hosted service are listed on the site
Thunderbird is a free email application that the site describes as easy to set up and customize. It offers a unified inbox or separate management of each account, plus calendars and contacts, tags and filtering, and extensions. It is available for Windows, macOS, Linux and Android.
The site says Thunderbird is Free and Open-Source Software released under the MPL 2.0 licence. The Thunderbird for Android repository states it is licensed under the Apache License, Version 2.0, and that the app is based on K-9 Mail, which joined the Thunderbird family in June 2022.
There is no price. Thunderbird is funded by user donations, and the site invites visitors to donate.
Thunderbird compared
Alternatives to Thunderbird
Microsoft's email and calendar app, with an ad-supported free version and ad-free Microsoft 365 plans.
- Freemium
Last updated 16 October 2026. Facts checked against the official site on 16 October 2026. How we make money