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Thunderbird vs Merkuro: catalog facts
Thunderbird	Merkuro
Free Free forever, funded by donations.	Free Free and open source under the GPL-3.0-or-later licence.
Windows, macOS, Linux, Android	Linux
Unified inbox across every account, or each account kept separate, your choice Mail, calendar, contacts and tasks in one application rather than four	Supports Nextcloud, Google Calendar, Outlook and CalDAV calendars Combines events, tasks and contacts in one app
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	Linux only Fits best within the KDE Plasma desktop
Downloadable app	Downloadable app
Open source	Open source
License: MPL-2.0	License: GPL-3.0-or-later
No account needed	Not stated if an account is needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 20, 2026	Official website Full listing and sources Checked October 1, 2026

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