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Exchange Calendar is an add-on for Thunderbird and Seamonkey.

It extends the Lightning add-on to provide Microsoft Exchange support.

Exchange Calendar extension can:

  • Synchronize calendars, tasks, and contacts with a Microsoft Exchange server.
  • Create, edit and update events and tasks.
  • Display contacts from your address books and the global address list (they are only readable, they are usable with address autocompletion).
  • Manage the Exchange « out of office » feature.

This extension requires:

  • Thunderbird between versions 52 and up to 59.
    • See the releases page for preview builds of ExchangeCalendar version 5 with Thunderbird 60 support.
  • Lightning extension corresponding to the Thunderbird release.
  • The targeted Exchange server has to provide an Exchange Web Service (EWS).

ExchangeCalendar is developed by a community of interested developers. Support is best effort and cannot be guaranteed. Contributions are welcome.


Download a pre-built release from our releases page or build your own release as shown below.

Development status

There is no active development at this time.

Thunderbird 68 compatibility

Currently not implemented. See issue #277.

A financial bounty is available for anyone who implements this support. For details and rules see the linked page.


This add-on was originally created by Michel Verbraak. It is open source and based on the work of many contributors.

Report issues

Please report any issues that have not previously been reported here.

The more information you can provide about an issue, the easier it becomes to reproduce and fix. Examples of helpful information are:

  • Thunderbird version
  • Lightning version
  • List of running Thunderbird add-ons
  • Log output

Patch the code

To help us to maintain the code, we will be thankful to follow these main guidelines:

  • Use indentation with 4 spaces
  • Avoid too long lines, try to break long lines into smaller ones
  • Avoid to write "spaghetti" code with too many if/else imbrications
  • Try to keep code simple to help us maintain it on long term

Note that our Makefile has a beautify target which will try to beautify all JavaScript (requires jsbeautifier Debian package) and XML code (requires tidy package) to help maintain a clean code.

When your patches are ready, you are welcome to do pull requests on our repository.

Please help us to review your code by making multiple small pull requests instead of big ones modifying big parts of the code.


You are welcome to provide translation updates on our Transifex project:

Build instructions

To manually build the add-on, you have to:

# clone this project
git clone
cd exchangecalendar
# build it
make build

Then an xpi file is created in the project folder. This file is directly installable from the add-on page of Thunderbird.

If it doesn't work, please check you have these tools installed (example for Debian):

sudo apt install git-core zip


This software is provided on a best-effort basis without any warranty. Please see the license for details.

Some of the icons and images used are from the Fugue Icons Collection made by Yusuke Kamiyamane.


Exchange Calendar, Tasks, Contacts provider for Mozilla Thunderbird







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  • JavaScript 98.5%
  • CSS 1.4%
  • Makefile 0.1%