eM Client vs Thunderbird on Windows (2026): Which to Pick

In the eM Client vs Thunderbird decision, pick Thunderbird if you want free and extensible, and eM Client if you want calendar, tasks and a finished interface. If you are on Windows 10 or 11 and searching emclient vs Thunderbird, that is the short version. The rest shows where the line falls for your setup, as of November 2026.

One thing changed recently and affects the answer. eM Client 11 shipped on 7 October 2026, with a much larger set of AI tools and Microsoft Graph support. That same month Microsoft began shutting down Exchange Web Services (EWS) on Microsoft 365, so if your mail is on Microsoft 365, read that row of the table first.

Which should you choose?#

Thunderbird is a good email client: the question is whether its strengths are the ones you need. Our Thunderbird review goes deeper. Find the column that sounds like you.

eM Client vs Thunderbird at a glance#

These are the differences that change a decision. Rows where the two match are left out: both support PGP and S/MIME, and both run on macOS. Check each vendor's site before you buy, because both are changing quickly.

Is eM Client or Thunderbird free?#

Thunderbird is free for anyone, including businesses, with no account limit. eM Client is free only for home use on two accounts and one device. Any commercial use, a third account or a second computer needs a paid licence. Those are sold as yearly subscriptions or one-time purchases.

The detail sits in our Thunderbird vs eM Client pricing comparison and our breakdown of eM Client's free and paid licences. Both vendors change terms, so check emclient.com/pricing for current limits. Thundermail, Thunderbird's paid service, does not change this: it is email hosting, not a paid version of the app.

Where Thunderbird wins#

Cost and control. The app has no licence to renew, and because it is open source no vendor can take it away or change the terms at the next version. A small business can install it on every PC at no charge, while eM Client needs a Business licence per device.

Extensions and Linux. Thunderbird's add-on catalogue is why experienced users stay: often one specific add-on has no equivalent elsewhere. eM Client has no comparable catalogue and no Linux build, so in a mixed Windows and Linux office, only Thunderbird runs on every machine.

Where eM Client wins#

Calendar and contacts. eM Client is closer to a personal information manager than a mail app, with calendar, contacts and tasks as core features, and Notes on paid tiers. Thunderbird's calendar handles invites and CalDAV but is plainer. The gap is widest on Microsoft 365, where Thunderbird currently syncs email only over Graph or EWS.

Mobile and AI. eM Client's free iOS and Android apps include calendar, contacts, tasks and notes, and you can move accounts from the desktop with a QR code. Thunderbird has a good Android app but no iPhone app yet. Version 11 also brings an AI sidebar assistant, a writing composer, summaries, natural-language search and AI-generated rules, with an option to connect your own AI provider. Thunderbird has no built-in equivalent: Assist, the experiment announced alongside Thundermail, is not listed at tb.pro, and its add-on listing says the private alpha has ended.

Moving from Thunderbird to eM Client#

eM Client has a Thunderbird import under File, then Import. Its documentation says it covers emails, events, tasks and rules, from whole accounts or selected folders. It does not mention contacts or signatures, so check those after importing. If your accounts are IMAP, you can also just add them and let the mail sync from the server.

Back up your Thunderbird profile first. If you are unhappy with Thunderbird but not sure about eM Client, there is a third path: Betterbird, a Thunderbird fork that runs on the same profile. We compare it and others in our list of more Thunderbird alternatives for Windows.

A third option, honestly#

AI Emaily is a different kind of tool, not a like-for-like replacement for either client, and we build it. It is an AI-native client with apps for Windows, Mac and iOS plus the web, across Gmail, Outlook and IMAP accounts. It triages mail, drafts replies from the Personal Context you write plus per-client profiles, and works in three modes: Manual, Copilot (you approve every send) and Autopilot (it handles routine mail within your rules, with undo and an audit log).

If you want a mature desktop client with deep calendar, a Linux build or add-ons, stick with the two above: Thunderbird's extensibility and eM Client's calendar depth are not things we compete with. If your real problem is keeping up with the same kinds of message, that is the question we built it for. Pro and Autopilot include a 7-day free trial, and there is no free plan.