Thunderbird is a free, open-source email client built by Mozilla, the same organization behind Firefox web browser. It's designed for people who want a fast, customizable inbox without ads, tracking, or a monthly subscription – and it works across Windows, Mac, and Linux, with an official Android app as well.
What Thunderbird does well
Combines multiple email accounts (Gmail, Outlook, Yahoo, and more) into one inbox
Built-in calendar, contacts, and RSS feed reader on desktop
Deep customization through themes and a large library of community add-ons
End-to-end encryption support (OpenPGP) built in natively
An official Android app (launched late 2024, built on the K-9 Mail codebase), with no cost and no ads
No ads and no business model based on monetizing your email data
Who it's for
Thunderbird suits people juggling several email accounts who want one place to manage all of them, privacy-conscious users who prefer a desktop email client over a cloud-based webmail experience, and anyone who prefers open-source software they can inspect and extend.
Getting started
Downloading and installing Thunderbird takes about five minutes: download the installer from Mozilla's official site, run it, and use the built-in account setup wizard to connect your existing email addresses – most major providers auto-configure without needing manual server settings.
Where Thunderbird still hits its limits
Thunderbird has closed some real gaps in the past couple of years – there's now an official mobile app for Android and F-Droid, for instance. But a few limitations remain, especially for anyone managing more than just a personal inbox:
There's still no iOS app. As of now, iPhone and iPad users are left out entirely, and Mozilla hasn't given a release date for one.
The Android app focuses mainly on core email. It currently doesn't include the desktop calendar or address book experience.
Chat support is limited to XMPP, IRC, Matrix, and Odnoklassniki – there's no built-in way to connect Slack or Microsoft Teams if that's where your team collaborates.
Thunderbird's Exchange support is primarily focused on email. Calendar and contacts still require separate solutions or add-ons, which are often paid.
There's no built-in notes feature.
There's no dedicated supportline if something breaks – you're relying on community forums and volunteer help.
If you've hit one of these walls – especially around calendar/contacts sync over Exchange, workplace chat, or needing your inbox and notes in one place – it's worth knowing what you'd gain by switching to eM Client:
Native iOS and Android apps, with calendar, contacts, tasks, and notes alongside email in the mobile app, not just email
Full Exchange support across email, calendar, and contacts – not just the inbox
Built-in chat that connects to Slack, Microsoft Teams, Rocket.Chat, IceWarp Teamchat, and via XMPP protocol – useful if your team already lives in one of those tools
A dedicated Notes feature that stores notes locally or syncs them via CalDAV or Exchange, so notes live next to your email instead of in a separate app
Built-in AI features for proofreading, translating, and drafting replies
Dedicated customer support (VIP support included with purchase) on top of a community forum
Start with the free license and upgrade only if you need more. Paid licenses unlock advanced productivity features such as Snooze, Watch for Reply, Undo Send, Mass Mail, Quick Actions, and much more. Business licenses also include centralized license management and admin tools through the License Manager.
FAQ
Is Thunderbird really free?
Yes, entirely free with no paid tiers or feature paywalls. Some add-ons can be paid, though.
Does Thunderbird work with Gmail and Outlook.com?
Yes, both connect natively through IMAP.
Does Thunderbird have a mobile app?
Yes – an official Android app has been available since late 2024, focused mainly on core email. There's currently no iOS app.
Does Thunderbird connect to Slack or Microsoft Teams?
No, its built-in chat only supports XMPP, IRC, Matrix, and Odnoklassniki.
Is Thunderbird safe?
As an open-source project maintained by Mozilla, its code is publicly auditable, and it has no ad-based business model. eM Client is not open-source but follows the same ad-free approach, so you won't find ads in either application.
What's a good next step if I've outgrown Thunderbird?
eM Client includes Thunderbird’s capabilities, such as PGP encryption, while giving you a modern, all-in-one experience. eM Client stores your local data on your device, cannot access the contents of your emails, never sells your data, and is completely ad-free. You can start with a free license and upgrade only if you need advanced productivity features or business tools. On top of that, you get native iOS and Android apps, full Exchange email, calendar, and contact support, built-in Slack and Microsoft Teams chat, notes, and responsive customer support.
Outgrown what Thunderbird can do? See what you're missing