What are the best open source alternatives to eM Client?

The top open source alternatives to eM Client include Mailspring. These tools offer similar functionality while being free and open source.

Why choose an open source alternative to eM Client?

Open source alternatives provide transparency, community support, no vendor lock-in, and often cost savings. You can customize the software to your needs and have full control over your data.

Are these eM Client alternatives really free?

Yes, all listed alternatives are open source and free to use. You may need to pay for hosting if you self-host, but the software itself is free.

Best Open Source eM Client Alternatives in 2026

Desktop email client for Mac, Windows, and Linux with unified inbox, read receipts, link tracking, send later, grammar checking, and contact enrichment.

Mailspring is a native desktop email client for Mac, Windows, and Linux, built for people who send a lot of email and want more than basic send-and-receive. It connects to Gmail, iCloud, Office 365, Fastmail, Yahoo, and any IMAP/SMTP provider, pulling everything into a single unified inbox.

The free tier covers most daily needs: multi-account support, advanced search across all accounts, undo send, grammar and spell checking (powered by LanguageTool), custom signatures, dark mode, and localization into 12 languages with right-to-left layout support for Hebrew and Arabic. It also translates incoming and outgoing messages between English, Spanish, French, German, Russian, and simplified Chinese directly inside the composer.

Mailspring Pro ($8/month) adds the features that matter for professional communication:

Read receipts and link tracking so you know when a message was opened and which links got clicks
Send later and snooze to schedule outbound email and resurface threads at the right time
Follow-up reminders to avoid letting important conversations go cold
Quick reply templates for reusing outreach that works
Contact and company profiles with bios, social links, timezone, headcount, and funding info pulled in alongside your conversations
Mailbox insights showing open rates, click rates, and your busiest email hours

Under the hood, Mailspring uses a native C++ sync engine rather than wrapping a browser, which keeps RAM usage roughly half that of comparable clients and launch time under a second. Email syncs directly via IMAP, CalDAV, and CardDAV, so your messages go from your mail provider to your machine without passing through Mailspring's servers.

Compared to something like Spark Mail or Mailbird, Mailspring's main differentiators are its open codebase, direct sync architecture, and the combination of tracking features with a genuinely fast native interface. It runs on Linux including ARM64 and Wayland, which few desktop email clients bother to support properly.

Over 800,000 users have downloaded it since launch, and it's maintained by a small independent team with no outside investors.