Pick Outlook if you work in Microsoft 365, want Word, Excel and OneDrive inside your inbox, or need Copilot to help you write. Pick Thunderbird if you want a free, open-source email app that doesn't collect your data, show ads or train AI on your messages, and runs on Windows, macOS and Linux. Both handle several accounts, calendars and contacts in one place.
I read Microsoft's Outlook page and its support pages on the new Outlook for Windows and Outlook versions, then Thunderbird's home and Who We Are pages. They're both email apps, but their business models shape almost everything else.
Outlook and Thunderbird compared
| Outlook | Thunderbird | |
|---|---|---|
| Maker | Microsoft | Thunderbird project, part of the Mozilla family |
| Accounts | Outlook.com, work or school, Gmail, Yahoo!, iCloud, IMAP | Several accounts, separately or in a unified inbox |
| Platforms | Windows, Mac, web and mobile | Windows, Linux, macOS, plus Thunderbird Mobile for Android |
| Extras | Word, Excel, PowerPoint, OneDrive, Copilot, focused inbox | Tags, filters, extensions, deep customisation |
| Privacy model | Scans attachments and links for threats; encryption options | Doesn't collect personal data or sell ads; funded by donations |
| Licence | Microsoft software and subscriptions | Free and open source, MPL 2.0 |
| Free option (as of October 2026) | Yes, new Outlook for Windows, mobile app and Outlook.com account | Yes, free and open source |
What Outlook brings
Microsoft pitches Outlook as email, calendars, contacts and to-do lists in one view, on desktop, mobile and web. It connects personal, work and school accounts, including Outlook.com, Gmail, Yahoo!, iCloud and other services. You get focused inbox, sweep and snooze to cut clutter, Word, Excel and PowerPoint from the inbox, links to OneDrive files, and Copilot to help draft messages.
There are now two Outlook apps on Windows, which can be confusing. Microsoft's support page explains that new Outlook for Windows is free to get, while classic Outlook is a desktop app included with many Microsoft 365 subscriptions and Office Home & Business. If you rely on public folders, Microsoft says to stay on classic Outlook, because the new one only offers limited support.
What Thunderbird stands for
Thunderbird is a free and open-source project founded in 2003 and part of the Mozilla family. It puts messages, calendars and contacts in one fast app, with a unified inbox or separate accounts, tags, filters and a lot of room to customise. It's funded by user donations, and its home page says it doesn't collect personal data, sell ads in your inbox or train AI on your private conversations.
Its licence, MPL 2.0, keeps it free, and an elected Thunderbird Council has guided the project since 2014. Thunderbird runs on Windows, Linux and macOS, and Thunderbird Mobile now brings it to phones.
The new Outlook question
If you're on Windows and comparing these two because Outlook changed, check which Outlook you have. Microsoft's version guide says new Outlook shows a Settings button in the top right; if it's missing, you're on classic Outlook. The new app supports most accounts, including Gmail, Yahoo!, iCloud and IMAP, so switching email apps isn't the only way to keep your mix of addresses together.
How to decide
- Live in Microsoft 365 at work? Outlook keeps email next to your documents and Teams.
- Want an email app with no ads and no data collection? Thunderbird.
- Use Linux? Thunderbird runs there; Outlook's web app is the Microsoft route.
- Depend on public folders? Microsoft says stay on classic Outlook.
- Want AI help writing emails? Outlook has Copilot; Thunderbird's focus is privacy.
If you're staying with Outlook, here's how to organise your Outlook inbox and export your Outlook contacts.
My advice on Outlook or Thunderbird
If your work runs on Microsoft 365, Outlook is the sensible default, and the free new Outlook for Windows means you don't have to pay just to use it. If you want an email app that's yours, with no ads, no data harvesting and freedom to customise, Thunderbird is a lovely choice, and it's free. I'd keep work email where your company's tools are, and give Thunderbird a go for everything personal.
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Frequently asked questions
Is Thunderbird free?
Yes. Thunderbird is free and open-source software under the MPL 2.0 licence, funded by user donations.
Is the new Outlook for Windows free?
Microsoft's support pages say you can get new Outlook for Windows for free. Classic Outlook is included with many Microsoft 365 subscriptions.
Can Outlook and Thunderbird use Gmail?
Yes. Microsoft says Outlook connects Gmail, Yahoo!, iCloud and IMAP accounts, and Thunderbird manages several accounts in one app.
Does Thunderbird collect my data?
Thunderbird says it doesn't collect or store your personal data unless you ask it to, and never sells it.
How can I tell new Outlook from classic Outlook?
Microsoft says new Outlook shows a Settings button in the top right corner. If it's missing, you're using classic Outlook.
