Thunderbird Desktop
Version 156.0beta | Released August 31, 2026
Check out the notes below for this version of Thunderbird. As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla.
These notes apply to Thunderbird version 156 beta 3 released September 8, 2026.
System Requirements: Details
What’s New
new
OpenPGP key properties can print debug information to the Error Console
new
External browser login flow enabled for Yandex
new
Custom OAuth support for issuer ID and client secret field for IMAP and POP3
new
Custom OAuth support for POP3
new
Enterprise policy DisableUpdateSettings prevents users from changing update settings
new
Enterprise policy DisableDataCollectionSettings prevents users from changing data collection setting
new
Enterprise policy DisableMessageForwardingFilters prevents message filters from automatically forwarding messages
What’s Changed
changed
Preference mail.offer_experimental_features renamed to mail.experimental_features_settings.enabled
What’s Fixed
fixed
Detached attachment links were truncated when folder path contained &
fixed
POP3 folders with names over 55 characters could become duplicated after upgrading
fixed
Folders with invalid filename characters could show hashed names if cache was lost
fixed
Save All, Detach All, and Delete All failed after deleting one attachment
fixed
Renaming folders could reset folder settings
fixed
Subscribing an IMAP folder and subfolder together failed to subscribe the subfolder
fixed
Some newly fetched POP messages were not marked with new star after startup
fixed
Sorting after deleting the only child message removed the parent from view
fixed
OpenPGP signing failed with external GnuPG when the primary key could not sign
fixed
Remote content could load in encrypted messages opened from files
fixed
Sent message with expired S/MIME certificate wrongly showed untrusted CA warning
fixed
PDF attachments from compose windows could wrongly be detected as HTML
fixed
Saving unconfirmed recipients could create invalid address pills with >>
fixed
External browser OAuth failed when a browser preconnection closed first
fixed
Pressing Enter on Windows system tray icon did not restore Thunderbird window
fixed
Inline attachments incorrectly changed the message channel content type
fixed
Message loading was slow while discovering large numbers of IMAP folders
fixed
SMTP authentication failed when usernames contained non-ASCII characters
fixed
Unsupported EWS archive folder prevented all mailbox folders from syncing
fixed
Case differences in CalDAV email addresses caused duplicate invitations
fixed
Accepted CalDAV invitations could be saved to the wrong calendar
fixed
Visual and UX improvements
Fixed in beta 2
What’s Fixed
fixed
Opening a PDF attachment in a tab displayed empty tab
Fixed in beta 3
What’s Changed
changed
Thundermail built-in add-on updated to v2.0.11
What’s Fixed
fixed
Empty filter search values matched every message
fixed
Users could not set up custom OAuth for Exchange accounts
fixed
Manual Get Messages failed after startup until toggling offline mode
