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Thunderbird Monthly Development Digest: November/December 2025

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Hello again from the Thunderbird development team as we start to wind down for the holidays! Over the past several weeks, our sprints have been focused on delivery and consolidation to clear our plates for a fresh start in the New Year. 

Following our successful in-person work-week to discuss all things protocol, we’ve brought Exchange support (EWS) to our Monthly release channel, completed much of the final phases of the Account Hub experience, and laid the groundwork for what comes next. Alongside this feature work, the team has spent a significant amount of time adapting to upstream platform changes and supported our Services colleagues as we prepared for wider rollout. It’s been a period of steady progress, prioritization, and planning for the next major milestones.

Exchange Email Support

Since the last update, we’re so happy to finally announce that Exchange support for email has shipped to the Monthly release channel, accompanied by supporting blog posts, documentation and some fanfare. In the weeks leading up to and following that release, the team focused on closing out priority items, addressing stability issues, and ensuring the experience scales well as more users add their EWS-based Exchange accounts.

Work completed during this period includes:

In parallel, the team has begun work on Graph API support for email, which is now moving rapidly through its early stages, thanks in large part to the solid foundation laid for EWS. It’s so nice when a plan comes together

This work represents the next major milestone for Exchange support and will inform broader architectural refactoring planned for future phases.

The Exchange team also met in person to plan out upcoming milestones. These sessions allowed us to break down future work and begin early research and prototyping for:

Keep track of our Graph API implementation here. 

Account Hub

A major focus during this period was completing the Email Account Hub Phase 3 milestone, with the final bugs landing and remaining items either completed or moved into maintenance. This work was prioritized to improve the experience for users setting up new accounts, particularly Exchange accounts.

Notable improvements and fixes include:

With the primary Phase 3 goals now complete, the team has been able to shift attention back to other front-end initiatives while continuing to refine the Account Hub experience through targeted fixes and polish.

Follow progress in the meta bugs for phase 3 and telemetry

Calendar UI Rebuild

Calendar UI work progressed more slowly during this period due to competing priorities (hiring!), in-person meetups and planned time off, but planning and groundwork continued and development back underway. The team:

Stay tuned to our milestones here:

Maintenance, Upstream adaptations, Recent Features and Fixes

Throughout this period, the team also spent a considerable amount of time responding to upstream changes that affected build stability, tests, and CI. Sheriffing remained challenging, with frequent tree breakages requiring investigation to distinguish upstream regressions from local changes. In addition to these items, we’ve been blessed with help from the larger development community to deliver a variety of improvements over the past two months. 

A very special shout out to a new contributor who worked with our senior team to solve a 19-year old problem relating to unread folders. Interactions like this are fuel for our team and we’re incredibly grateful for the help.

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.

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Toby Pilling

Senior Manager, Desktop Engineering

Tags: Account Hub Calendar Development Digest Exchange

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