Mozilla has been hard at work on the Thunderbird email app over the past year, with new features and interface improvements slowly rolling out. One more significant feature is now in the works: connecting to Microsoft Exchange servers.
Microsoft Exchange Server is a mail and calendar server developed by Microsoft, and often used to sync information for business or organization accounts, like work email accounts. Exchange has always worked with Microsoft’s own Outlook applications, as well as a few third-party applications like Apple Mail/Calendar, but there has never been full support in Mozilla Thunderbird. You can sometimes syncronize the mail component with Thunderbird and other email applications using standard IMAP, but that option isn’t always available.
Mozilla published a blog post summarizing Thunderbird’s development in 2023, which includes confirmation that Exchange support is on the way. The blog post explained, “Speaking of functionality you expect, we hear you loud and clear: you want Exchange support in Thunderbird. We’ve already done some exploratory work, and have enabled the usage of Rust in Thunderbird. This is a complex topic, but the short version is that this opens the doors for us to start implementing native support for the Exchange protocol. It’s officially on our roadmap!” The feature’s discussion thread on Bugzilla mentions that authentication, email calendar, and contacts are all planned to be supported.
The discussion thread reveals at least one catch, though. Mozilla is planning to implement Exchange support through Exchange Web Services (EWS for short), which Microsoft will no longer support in its hosted email servers (e.g. Microsoft 365 accounts) starting on October 1st, 2026. That means if the feature is implemented, it will only work with Microsoft-hosted Exchange accounts for a short time, depending on when it actually arrives in the email application. It will only work with self-hosted Exchange servers after that point, such as accounts operated on-site by organizations and businesses, which is not common these days—one estimate said 84% of Exchange deployments in 2023 were in Microsoft’s cloud services.
Sean Burke, a software engineer at Mozilla, said in the discussion thread, “At present, EWS is our best way to enable support for both Exchange Online and on-premise installations. Graph API has been considered and may be considered again in future, but it currently provides narrower support than EWS and lacks some functionality for desktop applications. Even with the announcement that EWS support will be removed for Exchange Online, it’s still valuable in the short term for enabling access for a wide userbase and in the long term for supporting users using on-premise installations.”
There’s no estimated release date right now for Exchange support in Thunderbird.
Source: Thunderbird Blog, Bugzilla
