Using open-source software in a corporate environment has always felt like trying to fit a square peg into a round hole. The “corporate requirement” — Microsoft Exchange — was the wall we couldn’t climb.
If you ran Linux or cared even a little about privacy, you had two bad choices. You either paid for a third-party plugin to paper over the gap or resigned yourself to keeping Outlook Web App (OWA) open in a bloated browser tab all day. I know that frustration well. It is exactly why I tell people: please stop using Outlook. Nothing breaks the illusion of a clean, carefully tuned desktop faster than a permanent browser window whose only job is to check whether your boss has emailed.
However, with the recent release of Thunderbird 145, the wall has finally come down. Mozilla has deployed native support for Microsoft Exchange. This isn’t a hack, nor is it a wrapper. It is a fundamental rebuild of how the client handles corporate mail. After spending time with the update, I was able to migrate my work setup to Thunderbird fully. This is the update many of us have been waiting for, and it fundamentally changes what using open source email at work can look like.
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Android, Windows, Linux & Mac
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Free (open-source)
Manage all your emails in one place with Thunderbird. This powerful, open-source client offers strong privacy controls and flexible account management.
Native Exchange support means no more paid add-ons
Rusty under the hood, shiny on the surface
Over the years, if you wanted to set up Exchange on Mozilla Thunderbird without enabling IMAP (which many corporate IT security policies disable), you had exactly one viable option: Owl for Exchange or ExQuilla.
Both did their job well, but they came up with compromises that never sat right. They are paid, closed-source, and subscription-based, which means you end up paying to make a free email client usable at work. There is also the lingering risk factor. If development ever stalls or support ends, your access to corporate email disappears with it.
I replaced my entire Microsoft Office subscription with free open-source apps
Office work should make you money, not cost it.
That entire equation changed with Thunderbird version 145, released in November 2025. Thunderbird now supports Microsoft Exchange natively. Mozilla didn’t just patch this in; rather, they rebuilt the protocol handling using Rust. This matters for a few critical reasons. First, the connection is significantly faster than previous IMAP implementations. Syncing feels instantaneous, mimicking Outlook’s “push” behavior rather than the sluggish polling of legacy protocols.
Second, Modern Auth (OAuth2) is standard for Microsoft 365 accounts. When you add your account, Thunderbird automatically detects the settings and presents the standard Microsoft login prompt (MFA and all). If you’re stuck on older corporate infrastructure, it even supports “on-premise” servers using Basic authentication.
There is a fascinating bit of future-proofing happening here, too. While this update utilizes EWS to ensure maximum compatibility right now, the developers have acknowledged that Microsoft is slowly phasing EWS out in favor of Microsoft Graph. Mozilla is already working on Graph support to meet Microsoft’s future deadlines, which means, more than just being a feature drop, it’s a long-term commitment to keeping your corporate email flowing.
It’s a huge leap for email, but the calendar still needs work
Don’t burn your browser tabs just yet — you’re going to need them for invites
The primary reason people stay glued to Microsoft Outlook isn’t usually the email — it’s the ecosystem. While the email side of the equation is now seamless in Thunderbird, it is important to temper expectations regarding the rest of the Office 365 suite. Even if you are ready to explore the best free alternatives to Microsoft Outlook, moving away from a deeply integrated workflow takes some adjustment.
The “Unified Inbox” dream is alive and well. I can now drag an email from my corporate inbox and drop it into a local folder for offline archiving, something that is notoriously difficult in webmail. I can search through gigabytes of old corporate mail instantly without waiting for a server query. However, if you live and die by your corporate schedule, you aren’t crossing the finish line just yet.
As detailed in the release notes, the native implementation in version 145 only covers Email (EWS). Your emails sync perfectly, folder management works, and the “Supernova” UI looks modern and professional. But native synchronization for calendars and address books is still on the roadmap for 2026. If you try to add your Exchange calendar right now, Thunderbird won’t see it natively. You will still need to use a workaround (such as the TbSync add-on, a must-have Thunderbird add-on) or keep your calendar open in a browser.
This one is for you on Linux. If you install Thunderbird via Flatpak, you are likely on the ESR (Extended Support Release) channel. This means you won’t see these new Exchange features until the next major ESR update, likely around mid-2026. To use this now, you need the monthly release version (tarball or .deb).
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A victory for open source, even if it’s currently fashionably late to the party
For me, the trade-off is worth it. Email is 90% of my day, and having that in a fast, distraction-free, open-source client improves how I work. If you’ve been holding out for a “perfect” all-in-one replacement for Outlook, you might want to wait for the 2026 updates. But if you want your work email to function without friction on your operating system of choice, Thunderbird 145 is the update that delivers.
