Latest version of Thunderbird released

Thunderbird 155.0 Final

What’s New

S/MIME popup shows signature, digest, encryption algorithms and key sizes
Default address book for manually added contacts configurable with mail.addr_book.add_item_default_uri
Enterprise policy DisableQRExport can disable QR export
OAuth add-ons can override built-in settings for selected domains and hostnames
Manual account config streamlined with Exchange, Graph, and custom OAuth support
Custom OAuth support for IMAP and SMTP servers
PKCE and external browser fields added to custom OAuth settings
Enterprise policy DisableExperimentalFeatures for disabling experimental features

What’s Fixed

Unread count dock badge disappeared on macOS restart when no mail window opened
IMAP tags did not sync automatically across clients
Embedded SVG images appeared broken when Display Attachments Inline was disabled
Holding arrow keys failed to smoothly navigate the folder pane
Mark and Tag menu bar items were disabled in search results
Quick Filter ignored address book display names shown in message lists and headers
Attachment filters could disappear or return no results in global search
Body search failed for quoted-printable messages ending on a soft line break
Failed encrypted send did not preserve draft
Failed account setup left an incoming server that blocked account recreation
Removing an account did not remove its OAuth token from the password manager
Account Hub prompted for calendar credentials immediately after successful login
Filters could copy empty messages to Local Folders during startup mail download
Closing message filters wrongly warned completed newsgroup filters were running
Autoscroll icon was missing directional arrows in scrollable messages
Apple Mail text attachments may not appear in MIME messages
Forwarded messages could display incorrect encoding
Thunderbird could crash due to improper database memory handling
Thunderbird could crash on shutdown while waiting for OAuth2 password entry
Thunderbird could crash while loading mail folders
Custom OAuth could not be disabled
Legacy IMAP tag changes were not sent to the server and reverted after refresh
Deleting an Exchange account retained the outgoing server settings
CalDAV calendars with offline support could stop fully synchronizing events
Offline cached ICS calendar changes were silently lost after reconnecting
Thunderbird upgrade disabled composition toolbar
Thunderbird upgrade disabled Settings menu for versions before macOS 13
Windows jump list menu no longer functioned correctly
Visual and UX improvements

Security fixes

Thunderbird 155.0.1 (Released September 9, 2026)

Fixed​

Empty filter search values matched every message

Thunderbird 156.0

What’s New

OpenPGP key properties can print debug information to the Error Console
External browser login flow enabled for Yandex
Custom OAuth support for issuer ID and client secret field for IMAP and POP3
Custom OAuth support for POP3
Enterprise policy DisableUpdateSettings prevents users from changing update settings
Enterprise policy DisableDataCollectionSettings prevents users from changing data collection setting
Enterprise policy DisableMessageForwardingFilters prevents message filters from automatically forwarding messages

What’s Changed

Preference mail.offer_experimental_features renamed to mail.experimental_features_settings.enabled

Thundermail built-in add-on updated to v2.0.11

What’s Fixed

Detached attachment links were truncated when folder path contained &
Opening a PDF attachment in a tab displayed empty tab
POP3 folders with names over 55 characters could become duplicated after upgrading
Folders with invalid filename characters could show hashed names if cache was lost
Save All, Detach All, and Delete All failed after deleting one attachment
Renaming folders could reset folder settings
Subscribing an IMAP folder and subfolder together failed to subscribe the subfolder
Some newly fetched POP messages were not marked with new star after startup
Sorting after deleting the only child message removed the parent from view
OpenPGP signing failed with external GnuPG when the primary key could not sign
Remote content could load in encrypted messages opened from files
Sent message with expired S/MIME certificate wrongly showed untrusted CA warning
PDF attachments from compose windows could wrongly be detected as HTML
Saving unconfirmed recipients could create invalid address pills with >>
External browser OAuth failed when a browser preconnection closed first
Users could not set up custom OAuth for Exchange accounts
Pressing Enter on Windows system tray icon did not restore Thunderbird window
Inline attachments incorrectly changed the message channel content type
Message loading was slow while discovering large numbers of IMAP folders
SMTP authentication failed when usernames contained non-ASCII characters
Unsupported EWS archive folder prevented all mailbox folders from syncing
Manual Get Messages failed after startup until toggling offline mode
Case differences in CalDAV email addresses caused duplicate invitations
Accepted CalDAV invitations could be saved to the wrong calendar
Visual and UX improvements

Security fixes

UniGetUI just found this and did the update.

Thunderbird 156.0.1
Fixed
Thunderbird could crash when saving a message

Thunderbird 157.0

Changelog:

What’s New

• Enterprise policy DisableChat disables Thunderbird Chat functionality
• Enterprise policy DisableFileLink disables Thunderbird FileLink functionality

What’s Changed

• Preference mailnews.headers.minNumHeaders has been removed
• Allow viewing remote content in OpenPGP messages encrypted with integrity protection
• RNP command-line utilities are no longer included with Thunderbird
• IMAP/POP manual config port field is now optional
• Thundermail built-in add-on updated to v2.0.16

What’s Fixed

• Ctrl+Shift+K could fail to open the Quick Filter UI
• Message list could show the wrong sender for messages
• Status bar could remain active and cause 100% CPU usage after activity ended
• OpenPGP discovery failed to find replacement keys after a key was revoked
• Valid RSA OpenPGP keys could be rejected, preventing encryption
• Sent messages could silently fail to save to the IMAP Sent folder
• Sending message did not fail gracefully with malformed references header
• Thunderbird could hang when waiting for IMAP server greeting during account setup
• Account Hub account creation could fail with malformed URI
• Custom OAuth Endpoint Host incorrectly required a full URL instead of a domain
• Message filters could falsely match when evaluating search term failures
• CardDAV address books could fail to sync when no password prompt was needed
• Yahoo emails appeared blank with MIME handlers disabled via mailnews.display.disallow_mime_handlers
• Pending moves within the same IMAP account could make messages disappear
• Inline images could disappear after editing and resaving drafts
• SMTP OAuth2 failed when large access token exceeded command line length limit
• Gmail OAuth2 authentication could intermittently fail on Windows
• Exchange NTLM authentication failed when updated passwords were not saved
• SMTP AUTH LOGIN could fail after username challenges and close the connection
• AppUpdatePin policy did not prevent Thunderbird from updating beyond pinned version
• Recurring events could appear after their configured end date
• CalDAV task body could remain outdated after syncing changes from another client
• CalDAV invitations could fail when accepted before the calendar synced
• Visual and UX improvements
• Security fixes

Thunderbird Eclipse 157.0.1