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Thunderbird vs Ltt.rs: catalog facts
Thunderbird	Ltt.rs
Free Free forever, funded by donations.	Free Free and open source under the Apache 2.0 licence.
Windows, macOS, Linux, Android	Android
Unified inbox across every account, or each account kept separate, your choice Mail, calendar, contacts and tasks in one application rather than four	Native JMAP support Simple, focused interface
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	Works only with JMAP servers, not IMAP Described as a proof of concept
Downloadable app	Downloadable app
Open source	Open source
License: MPL-2.0	License: Apache-2.0
No account needed	Not stated if an account is needed
Works offline	Needs internet
Official website Full listing and sources Checked September 20, 2026	Official website Full listing and sources Checked October 2, 2026

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