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Microsoft OutlookMailspring
Freemium

Free app and account available; Microsoft 365 plans add paid features and Office apps.

 Freemium

The client is free and open source. Mailspring Pro is a monthly subscription that adds…

Windows, macOS, Android, iOS, Web Windows, macOS, Linux
  • Email, calendar and contacts for multiple accounts in one app
  • Available on desktop, mobile and 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
  • Closed source and tied to Microsoft services
  • Some features, including Copilot, require a paid plan
  • Read receipts and link tracking are paid, and are tracking features
  • Electron, so still heavier than a native client
Downloadable app, Web application Downloadable app
Closed source Open source
License not stated License: GPL-3.0
Not stated if an account is needed No account needed
Not stated if it works offline Works offline

Checked September 23, 2026

Checked September 21, 2026

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