Lightning brings the Sunbird calendar to the popular email client, Mozilla Thunderbird.

Since it's an extension, Lightning is tightly integrated with Thunderbird, allowing it to easily perform email-related calendaring tasks.

Support the Lightning Team

Please support our efforts by donating to the Calendar Project.


Lightning is licensed under the MPL/GPL/LGPL triple license, allowing use of the files under the terms of any one of the Mozilla Public License, the GNU General Public License, or the GNU Lesser General Public License.

System Requirements:

Lightning is compatible with Thunderbird and SeaMonkey.

Lightning requires slightly more processing power and memory than the equivalent version of Thunderbird. Please check the Thunderbird or Seamonkey release notes for more details.

Downloading and Installing:

Before installing, make sure your computer meets the system requirements. provides Lightning for Windows, Linux and Mac OS X in a variety of languages. Windows users must have Windows XP or later.

IMPORTANT: Install the updated timezones for Windows XP or later. Information on obtaining the updated timezones can be found in Microsoft Knowledge Base article 955839. Not updating your Windows timezones will result in unreliable and erroneous display and entry of time data! Be sure to do this.

What's New:

  • New: File link attachments can now be linked to again instead of uploading them again
  • New: Mark all folders of an account as read
  • New: Run filters periodically. Improved filter logging.
  • New: OAuth2 authentication for Yandex
  • New: 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)
  • New: On Windows a 64bit installer and MSI package are now available, see the Thunderbird for Organisations page for details
  • New: Added a policy engine that allows customized Thunderbird deployments in enterprise environments, using Windows Group Policy or a cross-platform JSON file
  • New: TCP keepalive for IMAP protocol
  • New: Full Unicode support for MAPI interfaces: New support for MAPISendMailW
  • New: 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.
  • New: Calendar: Time zone data can now include past and future changes. All known time zone changes from 2018 to 2022 are included.
  • New: Chat: In each conversation an individual spellcheck language can be selected now
  • Changed: Add-on support: Add-ons are only supported if add-on authors have adapted them
  • Changed: Dictionary support: Only WebExtension dictionaries are supported now. Both and now provide WebExtension dictionaries.
  • Changed: Theme support: Only WebExtension themes are supported now. Both and now provide WebExtension themes.
  • Changed: The stand-alone options window has been removed, all options are now shown in a tab
  • Changed: Changed UI when installing add-ons
  • Changed: Various theme improvements including a dark message list/thread pane
  • Changed: Application menu aka "Hamburger menu"
  • Changed: Improvements when entering, selecting and removing recipients in the Write window
  • Changed: FileLink: WeTransfer is already included. Dropbox and using the New WebExtensions FileLink API are available as add-ons, amongst others.
  • Changed: 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
  • Changed: Composition text and background colors no longer sent by default. New option in "Tools > Options, Composition".
  • Changed: UI improvements for external and detached attachments, now showing as links with New menu option "Open Containing Folder"
  • Changed: Textual attachments (plain text, HTML, XML, etc.) are no longer displayed inline. Toggle preference mail.inline_attachments.text to display them inline again.
  • Changed: Improved phishing attempt detection for messages with certain forms
  • Changed: Improvements to scam warnings
  • Changed: Reply to self will now search all identities (default of preference mailNews.reply_to_self_check_all_ident Changed to true)
  • Changed: Maildir now uses the message ID as file name and "eml" as file extension
  • Changed: Auto-compact threshold increased from 20 MB to 200 MB
  • Changed: Calendar: UI improvements for event dialog
  • Changed: Calendar: Thunderbird's calendar add-on Lightning now uses the same version numbering scheme
  • Changed: Thunderbird 68 distrusts most SSL/TLS certificates issued by the Certificate Authorities (CA) with the brand names Symantec, GeoTrust, RapidSSL and Thawte. Consequently, any SSL/TLS connections to servers using an affected certificate will fail. Affected servers must be updated to use a different certificate. If Thunderbird displays an error message which states that an additional policy constraint has failed, you should check if the server uses a certificate issued by one of the mentioned brands. Additional information on Mozilla's action is available at here.
  • Fixed: Column choice and sort order in "Search Messages" dialog lost after relaunch
  • Fixed: Global indexer causing high CPU loads under some circumstances
  • Fixed: Tags set on IMAP folders sometimes not visible to other users
  • Fixed: "Contribute" button in add-on details not working
  • Fixed: SMTP password wasn't removed when account was deleted or server or user name were Changed
  • Fixed: Mbox to Maildir conversion not working if Windows search integration is enabled
  • Fixed: Mails won't get removed from Trash folder using Maildir. Note: Other deletion issues related to Maildir may still persist.
  • Fixed: When sending of a message failed due a security issue, only "unknown error" was displayed. Now more details are given.
  • Fixed: Improvements of SMTP 5.7.1 message
  • Fixed: Calendar: Multiple connections with different users to the same CalDAV server not working
  • Fixed: Chat: Fixed XMPP authentication when using SASL

Known Issues

  • Unresolved: Edit tag not working (will be fixed in version 68.1)
  • Unresolved: Moving messages from "Search Messages" result dialog not working (will be fixed in version 68.1)
  • Unresolved: Issues with list of content types/actions for incoming attachments (will be fixed in version 68.1)