Thunderbird 68.0

What's new in this version:

New Features:
- File link attachments can now be linked to again instead of uploading them again
- Mark all folders of an account as read
- Run filters periodically. Improved filter logging
- OAuth2 authentication for Yandex
- Language packs can now be selected in the Advanced Options. Preference intl.multilingual.enabled needs to be set (and possily also extensions.langpacks.signatures.required needs to be set to false)
- On Windows a 64bit installer and MSI package are now available, see the Thunderbird for Organisations page for details
- Added a policy engine that allows customized Thunderbird deployments in enterprise environments, using Windows Group Policy or a cross-platform JSON file
TCP keepalive for IMAP protocol
- Full Unicode support for MAPI interfaces: New support for MAPISendMailW
- To protect your profile data against a downgrade, Thunderbird 68 may display a message "You have launched an older version of Thunderbird" and will not allow opening a specific profile. Workaround: start with option --allow-downgrade. See this support article for details
- Calendar: Time zone data can now include past and future changes. All known time zone changes from 2018 to 2022 are included
- Chat: In each conversation an individual spellcheck language can be selected now

Improved:
- Add-on support: Add-ons are only supported if add-on authors have adapted them
- Dictionary support: Only WebExtension dictionaries are supported now. Both addons.mozilla.org and addons.thunderbird.net now provide WebExtension dictionaries
- Theme support: Only WebExtension themes are supported now. Both addons.mozilla.org and addons.thunderbird.net now provide WebExtension themes
- The stand-alone options window has been removed, all options are now shown in a tab
- Changed UI when installing add-ons
- Various theme improvements including a dark message list/thread pane
- Application menu aka "Hamburger menu"
- Improvements when entering, selecting and removing recipients in the Write window
- FileLink: WeTransfer is already included. Dropbox and Box.com using the new WebExtensions FileLink API are available as add-ons, amongst others
- Text and background colors in the Write window and custom colors for tags are no longer restricted to a fixed 10x7 matrix of HTML colors
- Composition text and background colors no longer sent by default. New option in "Tools > Options, Composition"
- UI improvements for external and detached attachments, now showing as links with new menu option "Open Containing Folder"
- Improved phishing attempt detection for messages with certain forms
- Improvements to scam warnings
- Reply to self will now search all identities (default of preference mailnews.reply_to_self_check_all_ident changed to true)
- Maildir now uses the message ID as file name and "eml" as file extension
- Auto-compact threshold increased from 20 MB to 200 MB
- Calendar: UI improvements for event dialog
- Calendar: Thunderbird's calendar add-on Lightning now uses the same version numbering scheme

Fixed:
- Column choice and sort order in "Search Messages" dialog lost after relaunch
- Global indexer causing high CPU loads under some circumstances
- Tags set on IMAP folders sometimes not visible to other users
- "Contribute" button in add-on details not working
- SMTP password wasn't removed when account was deleted or server or user name were changed
- Mbox to Maildir conversion not working if Windows search integration is enabled
- Mails won't get removed from Trash folder using Maildir. Note: Other deletion issues related to Maildir may still persist.
- When sending of a message failed due a security issue, only "unknown error" was displayed. Now more details are given.
- Improvements of SMTP 5.7.1 message
- Calendar: Multiple connections with different users to the same CalDAV server not working
- Chat: Fixed XMPP authentication when using SASL