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Mailspring vs KMail: catalog facts
Mailspring	KMail
Freemium The client is free and open source. Mailspring Pro is a monthly subscription that adds…	Free Free and open source under the GPL.
Windows, macOS, Linux	Linux
Unified inbox, snooze, send later, rules and templates in the free tier C++ sync engine keeps memory and battery use down for an Electron app	OpenPGP and S/MIME encryption integrated rather than bolted on Shares contacts and calendar with the rest of the Kontact suite
Read receipts and link tracking are paid, and are tracking features Electron, so still heavier than a native client	Depends on the Akonadi storage service, which is a common source of problems Linux only in practice
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: GPL-2.0
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 21, 2026	Official website Full listing and sources Checked September 22, 2026

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