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Mailspring vs Microsoft Outlook: catalog facts
Mailspring	Microsoft Outlook
Freemium The client is free and open source. Mailspring Pro is a monthly subscription that adds…	Freemium Free app and account available; Microsoft 365 plans add paid features and Office apps.
Windows, macOS, Linux	Windows, macOS, Android, iOS, Web
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	Email, calendar and contacts for multiple accounts in one app Available on desktop, mobile and web
Read receipts and link tracking are paid, and are tracking features Electron, so still heavier than a native client	Closed source and tied to Microsoft services Some features, including Copilot, require a paid plan
Downloadable app	Downloadable app, Web application
Open source	Closed source
License: GPL-3.0	License not stated
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 23, 2026

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