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Microsoft Outlook vs Thunderbird: catalog facts
Microsoft Outlook	Thunderbird
Freemium Free app and account available; Microsoft 365 plans add paid features and Office apps.	Free Free forever, funded by donations.
Windows, macOS, Android, iOS, Web	Windows, macOS, Linux, Android
Email, calendar and contacts for multiple accounts in one app Available on desktop, mobile and web	Unified inbox across every account, or each account kept separate, your choice Mail, calendar, contacts and tasks in one application rather than four
Closed source and tied to Microsoft services Some features, including Copilot, require a paid plan	The interface carries a lot of history and can feel dense next to a webmail tab Major ESR releases have historically been disruptive for add-ons and settings
Downloadable app, Web application	Downloadable app
Closed source	Open source
License not stated	License: MPL-2.0
Not stated if an account is needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 20, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.