Mailspring
Open-source, cross-platform email client with unified inbox, snooze, and read receipts.
About
Mailspring is the open-source email client for Mac, Windows, and Linux, maintained by one of the original authors of Nylas Mail. It replaced Nylas's JavaScript sync code with a C++ sync engine built on Mailcore2, which runs locally and idles with near-zero CPU — your email credentials are never sent to a cloud server. It supports all IMAP providers including Gmail, Office 365, and iCloud, with unified inbox, snooze, send later, mail rules, templates, and offline search.
The UI is GPLv3 and the code lives on GitHub (Foundry376/Mailspring, ~17.9k stars, actively maintained with releases into October 2026). Core features are free; Mailspring Pro at $8/month adds link tracking, read receipts, mailbox analytics, and contact/company profiles. The honest caveat from users: syncing quirks and limited support infrastructure compared with commercial clients.
What it can do
- Unified inbox with offline search and mail rules
- Local C++ sync engine — credentials never leave the device
- Snooze, send later, templates, and Gmail labels support
- Read receipts and link tracking (Pro)
- Plugin architecture with open-source GPLv3 code
Setup
Download the installer for Mac, Windows, or Linux and connect any IMAP account; unlock Pro in-app if needed.
Prerequisites
An IMAP email account; $8/mo Pro for tracking, analytics, and advanced sending features.
Use cases
Works with
Trust score — 8/10
Scored 8/10 (verified tier, metrics-v1). Evidence: Open-source fork of Nylas Mail by original author; local C++ sync engine, no cloud credential storage; GitHub Foundry376/Mailspring: ~17.9k stars, release 1.21.0 (May 2026), commits through Oct 2026; Free core; Pro $8/mo (tracking, analytics); user reports of sync quirks are the main caveat. License: GPLv3 (UI and C++ sync engine confirmed on GitHub).
★ 17,920 GitHub stars
How the trust score is built
Full methodology →- Adoption · stars/downloads, log-scaled vs peers
- 7.0/10
- Maintenance · recency, releases, issue load
- 8.0/10
- Openness · license + docs
- 10.0/10
- Manual review · sanity read + red-flag check
- 8.0/10
- · Open-source fork of Nylas Mail by original author; local C++ sync engine, no cloud credential storage
- · GitHub Foundry376/Mailspring: ~17.9k stars, release 1.21.0 (May 2026), commits through Oct 2026
- · Free core; Pro $8/mo (tracking, analytics); user reports of sync quirks are the main caveat
Sources
Every fact above was checked against these sources. Where a claim comes from the provider and couldn't be independently verified, the text says so.