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Mailspring vs Polymail: catalog facts
Mailspring	Polymail
Freemium The client is free and open source. Mailspring Pro is a monthly subscription that adds…	Paid Paid plans with a free trial.
Windows, macOS, Linux	macOS, iOS
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	Read tracking and follow-up reminders inside email Several inboxes in one place
Read receipts and link tracking are paid, and are tracking features Electron, so still heavier than a native client	Requires a paid subscription after the trial Read tracking may not suit privacy-minded recipients
Downloadable app	Downloadable app, Hosted service
Open source	Closed source
License: GPL-3.0	License not stated
No account needed	Account 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 October 2, 2026

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