Roadmap

Below are the large projects planned for the 114 (2023) release of Thunderbird.
Firefox Sync
Accounts and syncing options in 114.
Expected Delivery: Q4 2022
Syncing between Thunderbird installations and the Android app should work seamlessly. Tags, filters, email accounts and relevants settings should be synced.
Unified Toolbar
Expected Delivery: Q4 2022
A single, reusable, global toolbar that is present throughout the app and acts as a simple interaction point for searching, interacting with the app menu and tab management.
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App Menu
The expanded app menu in 114.
Expected Delivery: Q3 2022
A single menu for the app that replaces the current hamburger menu, but also handles accounts and syncing.
Mail Tab Redesign
Expected Delivery: Q4 2022/Q1 2023
Update the Mail space with improved UX and UI, some of these enhancements include multi-line message list and "conversational" threads. It will be possible to reply to messages in the conversations area.
Depends On:
"Conversational" View
Expected Delivery: Q4 2022
 By default, Thunderbird users should be able to see all messages in a thread as a "conversation". With each message in that thread collapsible and expandable, with all messages showing up in that thread regardless of what folder they exist within.
1686504 - Thunderbird should have Conversations function built-in by default
Bug for conversations in Thunderbird
Global Message Index
Expected Delivery: Q4 2022
In order to do Conversations correctly, we need to be able to keep track of what folders messages in a thread are in, so we can display them in a conversation. This means we need to have a database that keeps track of the location of all emails.
3Pane (replacing XUL tree)
Expected Delivery: Q4 2022
Drop Window
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Link Preview Card Improvements
Link Preview Card (WIP)
Link previews should be improved to be more useful and visually appealing.
1572648 - Support rich embedding (previews) of links in composed content (Twitter Card, Open Graph data)
Link Preview Card tracking bug.
Account Setup Hub
Expected Delivery Q4 2022
The new Account Setup Hub
When setting up an email, autodiscovery of calendars and address books works really well! But managing accounts and setting up after the first time has lagged. We are updating that experience in 114 with a centralized place to set up accounts, with a consistent experience regardless of when you bring a new account into Thunderbird.
1664179 - (new-account-hub) [meta] implement account hub in tab
Account setup hub tracking bug.
Customizable Shortcuts
Expected  Delivery: Q4 2022
Calendar UI
Expected Delivery: Q1 2023