Mozilla Thunderbird 152 is now available as the latest stable release of the open-source email, calendar, contacts, and chat client, introducing one-click account setup for Thundermail accounts
The release also adds support for SecurityDevices in enterprise policies, providing administrators with an additional policy-controlled option for managed Thunderbird deployments.
Another key update is the adoption of PKCE for Gmail OAuth, an OAuth security extension that strengthens authorization flows, particularly when client secrets cannot be securely stored.
The mail server hostname is now verified when detecting address books and calendars, and the about page now uses a hosted URL instead of a local one. Plus, task handling has been improved so that the “Hide completed tasks” option now also hides canceled tasks.
On the bug-fixes side, this release resolves an issue where new mail alerts appeared on the wrong monitor in three-monitor setups and addresses a problem where spam messages triggered new mail notifications before being moved to the Spam folder.
Several subscription and newsgroup issues have been addressed as well. Filtered IMAP or NNTP subscriptions are now retained after closing the Subscribe dialog, and the “Download Headers” dialog for newsgroups opens as expected.
Threading and message display have received multiple fixes. Thunderbird 152 resolves issues with messages nested beyond 255 levels disappearing from the threading view, view corruption after deleting and undoing deletion of a thread parent, and single messages appearing collapsible after thread members were deleted.
Additionally, threads now update their order correctly without requiring a folder refresh or resort, and non-threaded subject sorting no longer separates “RE:” replies from their original messages.
Search functionality has been improved, as the release fixes body searches that missed draft messages containing German umlauts and addresses a crash that could occur during local message searches.
Microsoft account and Exchange users receive several important corrections. Thunderbird 152 fixes Microsoft OAuth2 failures when the HTTPS localhost redirect was not intercepted, resolves a problem where forwarding or redirecting Exchange messages failed with an out-of-memory error, and corrects cases where EWS messages could disappear from the folder view.
It also fixes Microsoft 365 bulk removal when trying to delete more than 1,000 messages at once and corrects EWS Trash behavior so folders already in Trash are hard deleted instead of being moved to Trash again.
Regarding the IMAP and POP3 handling, the “Show only subscribed folders” IMAP option can now be changed without restarting Thunderbird. Repeated IMAP notifications for messages read on another device after sleep or wake have been fixed, and a POP3 deadlock has been resolved for cases where a server became unresponsive without closing the socket.
Calendar fixes include improved handling of invitation acceptance, so Thunderbird now correctly distinguishes between a single occurrence and an entire series. The release also resolves transparent popups on macOS that hindered event editing, prevents duplicate attendees from being added to invitations, and preserves task percentage completion separately from status in tooltips.
Additional fixes address contact photo pasting, compose window behavior after NNTP failures, background sending, blocked file warnings, filter dialog accessibility, stale unread counts, MIME handling, visual and user experience improvements, and security issues.
For additional details, see the release notes. Mozilla Thunderbird 152 is available for direct download for Windows 10 and newer, macOS 10.15 and later, and Linux systems from thunderbird.net.
