The new update of the open source email client Thunderbird has arrived with its version 137, and while it doesn't incorporate major new features, it does include a large number of fixes and technical improvements aimed at optimizing the user experience. This version also comes with strategic announcements from Mozilla aimed at transforming this software into a more modern and competitive communications tool in the coming months.
Thunderbird 137 has been rated as an intermediate version, according to its roadmap, and is not part of the ESR (Extended Support Release) channel. This means its updates will be maintained for a limited period, until the arrival of the next monthly release, thus aligning with the new rapid release schedule recently adopted.
Technical improvements and bug fixes in Thunderbird 137
One of the main focuses of this version has been the debugging and improving overall client performanceIn total, more than 30 technical issues have been fixed, many of them related to message display, high-contrast mode notifications, and IMAP functionality. File support has also been improved. .eml In profiles with multiple folders, an issue that caused slowness when opening these types of files was fixed. For more details on previous versions, you can consult version 136.
For Linux users, the system tray icon has been temporarily disabled. until more comprehensive functionality is implemented. In the case of Windows, file names are now used when saving mail folders, which improves integration with the operating system and reduces errors related to file management.
The RSS have also received significant adjustments, now allowing the use of the space bar to scroll through messages, just like with emails. This small improvement facilitates more fluid navigation between informative content.
Searching in conversation mode has been optimized to correctly display results when sorted by date. Persistent issues such as IRC channels disappearing after a restart or incorrect MIME type assignment when forwarding emails as attachments have also been fixed.
Enhanced security in Thunderbird 137
Security has been an essential aspect in this versionAt least seven vulnerabilities of varying severity have been fixed, some of them classified as high risk. These included issues related to memory management, secure local file execution, and improper handling of Unicode characters that could lead to visual spoofing in the address bar.
In the field of encryption, Key aspects of OpenPGP support have been polishedIt is now possible to import public keys containing spaces without errors, and the inability to open messages has also been fixed. .eml digitally signed. Additionally, the option to decrypt and save attachments via right-click now works correctly.
Users working with services like Office 365 now have better support for two-factor authentication.This feature, which had been experiencing issues using OAuth2, has been fixed, and issues with contact servers like Radicale have also been resolved.
Visual Settings and User Experience in Thunderbird 137
Thunderbird 137 includes several visual changes and improvements in the user experience. Fixed a bug with line spacing within the message list when using the default font size, and also adjusted aspects of the account wizard for feeds, such as improperly spaced navigation buttons.
Issues in the configuration interface were identified and resolved which caused the menu to load multiple times and some text strings to appear in incorrect locations in the message security panel.
Moreover, Increased efficiency when moving bulk messages within IMAP accounts or to local folders, and fixed problems with automatic folder compression in case of occasional failures, trying to cover all possible directories.
Thunderbird as a comprehensive platform: Pro services arrive
Beyond the technical aspect, Mozilla has unveiled plans to take Thunderbird beyond the standard email client.Aware of the steady loss of users to closed platforms like Gmail or Microsoft 365, the organization aims to regain that ground by offering a complete communications ecosystem under an open license.
Under the name "Thunderbird Pro", Mozilla plans to introduce several paid professional services. Among them are:
- Thundermail: Mail hosting service based on the Stalwart stack, with support for the JMAP protocol, an alternative to the traditional IMAP.
- Thunderbird Send: A file sharing system based on the defunct Firefox Send, improved and adapted for greater flexibility.
- Thunderbird Appointment: Tool for planning appointments and events.
- Thunderbird Assist: An AI-powered assistant that can run locally or rely on the Flower Labs cloud, depending on the user's hardware.
All these services will initially be available free of charge to the community involved in the project., although a freemium model is expected to be adopted in the future, with storage limitations or other conditions for the free versions. Mozilla has also indicated the possibility that some of these services could be self-managed by advanced users to maintain autonomy from the cloud.
No specific date has been specified for the arrival of these new services., although statements by Ryan Sipes, head of the product, point to a near future in which Thunderbird could become a more complete bet within the free software landscape.
A new model of continuous development
Since February 2025, Mozilla has changed the Thunderbird release model to a monthly cycle., just as is already the case with Firefox. Thanks to this new dynamic, users receive improvements and fixes more quickly, reducing the wait for major annual updates.
This strategy seeks to maintain the competitive pace of the software against other commercial solutions., and also allows developers to introduce fixes more quickly, as reflected in version 137.0 with more than thirty identified and resolved issues.
Thunderbird 137 is available as a standalone binary package at their official website, allowing its use on most GNU/Linux distributions without installation, in addition to being available for macOS (from Catalina 10.15) and Windows (from Windows 10).
Thunderbird continues to demonstrate that it's not only a well-established tool within the free software space, but also maintains a clear ambition for evolution. This version 137, although lacking in striking new features, is a clear example of the effort to refine the experience for current users and pave the way for a new era with integrated services and expanded capabilities.
