• Development

Thunderbird Monthly Development Digest: February 2026

Welcome back to the Thunderbird blog and the first post of 2026! We’re rested, recharged, and ready to keep our community updated on all of our progress on the desktop and mobile clients and with Thunderbird Pro!

Hello again from the Thunderbird development team! After a restful and reflective break over the December holidays, the team returned recharged and ready to take on the mountain of priorities ahead.

To everyone we met during the recent FOSDEM weekend, thank you! The conversations, encouragement, and thoughtful feedback you shared were genuinely energizing, and many of your insights are already helping us better understand the real-world challenges you’re facing. The timing couldn’t have been better, as FOSDEM provided a strong early-year boost of inspiration, collaboration, and perspective.

FOSDEM – Collaboration, learning and real conversations

This year, a larger contingent of the Thunderbird team joined our Mozilla colleagues in Brussels for an intense and rewarding FOSDEM weekend. Across talks, hallway chats, and long discussions at the Thunderbird booth, we dug into standards, shared hard-won lessons, debated solutions, and explored what’s next for open communication tools.

The highlight, as always, was meeting users face-to-face. Hearing your stories about what’s working, what’s painful, and what you’d like to see next continues to be one of the most motivating parts of our work.

Several recurring themes stood out in these discussions, and we’re keen to help move the needle on some of the bigger, knottier challenges, including:

• Unblocking Oauth issues for Microsoft exchange
• Enterprise management feature support and extension
• Add-ons and feature requests to enable the continued move to FOSS solutions for many European institutions and orgs

These conversations don’t end when FOSDEM does but help shape our priorities for the months ahead, and we’re grateful to everyone who took the time to stop by, ask questions, or share their experiences.

Exchange Email Support

After releasing Exchange support for email to the Monthly release channel, we’ve had some great feedback and helpful diagnosis of edge case problems that we’ve been prioritizing for the past few weeks

Work completed during this period includes:

• Concurrency, queuing and prioritization of requests
• Classless folder handling
• Subfolder copy/move operations
• Starring a message (which proved to be far more painful than imagined)
• Custom Oauth configuration support

Work on supporting the Graph API protocol for email is moving steadily through the early stages, with these basic components already shipped to Daily:

• Initial scaffolding & rust crates
• Account Hub changes to support the addition of Graph protocol
• Login via Oauth
• Connectivity check

Keep track of our Graph API implementation here. 

Account Hub

The team met in person following FOSDEM and have planned out work to allow the new Account Hub UX to be used as the default experience in our next Extended Support Release this summer, which will ensure users benefit from changes we’ve made to enable custom Oauth settings and configuration specific to Microsoft Exchange.

Follow progress in the meta bugs for the last few pieces of phase 3 and telemetry, as well as the work we’ve defined to enable an interim experience for users setting up Thunderbird for the first time.

Calendar UI Rebuild

The new Calendar UI work has advanced at a good pace in recent weeks and the team met in person to break the work apart into chunks which have been prioritized alongside some of the “First Time User Experience” milestones. The team has recently:

• Completed sprint planning for upcoming milestones
• Assigned tasks and estimated work for the next 2 milestones
• Continued preparation for adopting Redux-based state management during the “Event Add/Edit” milestone

Stay tuned to our milestones here:

• Event Read Dialog
• Event Read Enhancements
• Read Dialog inline editing
• Event Add/Edit Dialog
• Reminders UI
• Invitations Dialog
• Calendar Views

Maintenance, Upstream adaptations, Recent Features and Fixes

Over the past couple of months, a significant portion of the team’s time has gone into responding to upstream changes that have impacted build stability, test reliability, and CI. Sheriffing continues to be a challenge, with frequent breakages requiring careful investigation to separate upstream regressions from Thunderbird-specific changes.

Alongside this ongoing maintenance work, we’ve also benefited greatly from contributions across the wider development community. Thanks to that collective effort, a steady stream of fixes and improvements has landed.

More broadly and focusing on our roadmap, the last two months have seen solid progress on Fluent migrations, as well as planning and early groundwork for rolling out Redux and the Design System more widely across the codebase.

Support from the community and team has resulted in some notable patches landing in recent weeks, with the following of particular help:

• Fixing unified toolbar sizing
• Hardening local search against crashes
• Migration of strings to modern Fluent –  Filters & Plurals
• and many more which are listed in release notes for beta.

If you would like to see new features as they land, and help us find some early bugs, you can try running daily and check the pushlog to see what has recently landed. This assistance is immensely helpful for catching problems early.

Toby Pilling

Senior Manager, Desktop Engineering