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Becky! Internet Mail vs Thunderbird: catalog facts
Becky! Internet Mail	Thunderbird
Paid Shareware that requires a paid licence after evaluation.	Free Free forever, funded by donations.
Windows	Windows, macOS, Linux, Android
Small, fast native Windows program Multiple mailboxes with separate profiles	Unified inbox across every account, or each account kept separate, your choice Mail, calendar, contacts and tasks in one application rather than four
Windows only HTML mail relies on an Internet Explorer component	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	Downloadable app
Closed source	Open source
License not stated	License: MPL-2.0
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked September 20, 2026

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