Thunderbird Desktop
Version 155.0 | Released September 1, 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.
System Requirements: Details
- Windows: Windows 10 or later
- Mac: macOS 10.15 or later
- Linux: GTK+ 3.14 or higher
What’s New
new
S/MIME popup shows signature, digest, encryption algorithms and key sizes
new
Default address book for manually added contacts configurable with mail.addr_book.add_item_default_uri
new
Enterprise policy DisableQRExport can disable QR export
new
OAuth add-ons can override built-in settings for selected domains and hostnames
new
Manual account config streamlined with Exchange, Graph, and custom OAuth support
new
Custom OAuth support for IMAP and SMTP servers
new
PKCE and external browser fields added to custom OAuth settings
new
Enterprise policy DisableExperimentalFeatures for disabling experimental features
What’s Fixed
fixed
Unread count dock badge disappeared on macOS restart when no mail window opened
fixed
IMAP tags did not sync automatically across clients
fixed
Embedded SVG images appeared broken when Display Attachments Inline was disabled
fixed
Holding arrow keys failed to smoothly navigate the folder pane
fixed
Mark and Tag menu bar items were disabled in search results
fixed
Quick Filter ignored address book display names shown in message lists and headers
fixed
Attachment filters could disappear or return no results in global search
fixed
Body search failed for quoted-printable messages ending on a soft line break
fixed
Failed encrypted send did not preserve draft
fixed
Failed account setup left an incoming server that blocked account recreation
fixed
Removing an account did not remove its OAuth token from the password manager
fixed
Account Hub prompted for calendar credentials immediately after successful login
fixed
Filters could copy empty messages to Local Folders during startup mail download
fixed
Closing message filters wrongly warned completed newsgroup filters were running
fixed
Autoscroll icon was missing directional arrows in scrollable messages
fixed
Apple Mail text attachments may not appear in MIME messages
fixed
Forwarded messages could display incorrect encoding
fixed
Thunderbird could crash due to improper database memory handling
fixed
Thunderbird could crash on shutdown while waiting for OAuth2 password entry
fixed
Thunderbird could crash while loading mail folders
fixed
Custom OAuth could not be disabled
fixed
Legacy IMAP tag changes were not sent to the server and reverted after refresh
fixed
Deleting an Exchange account retained the outgoing server settings
fixed
CalDAV calendars with offline support could stop fully synchronizing events
fixed
Offline cached ICS calendar changes were silently lost after reconnecting
fixed
Thunderbird upgrade disabled composition toolbar
fixed
Thunderbird upgrade disabled Settings menu for versions before macOS 13
fixed
Windows jump list menu no longer functioned correctly
fixed
Visual and UX improvements
