In order to integrate Thunderbird with Office 365 Calendar, you will need to download and install few additional plugins for Thunderbird.
Although the instructions and samples were created setting up Thunderbird on a Ubuntu Linux based system, the process with be similar across all other operating systems (i.e. Windows, Mac OSX ).
The Thunderbird email client does not come pre-packaged with a calendar option, however there are plenty of free Extensions you can download to incorporate a calendar feature.
The preferred calendar add-on is Lightning which allows you to organize your schedule directly within Thunderbird.
Install Lightning calendar in Thunderbird
Lightning calendar helps to organize your schedule and important events in a calendar that’s fully integrated with your Thunderbird or Seamonkey email client.
It enables you to manage multiple calendars, create your daily to do list, invite friends to events, and subscribe to public calendars. For more information check out the Lightning Calendar product page
In order to install the lightning plugin. Navigate to Tools –> Add-ons on your Thunderbird Menu.
In the search box search for lightning
This should return a few results, so pick the top one. at the time of writing this was Lightning and click install, once the install is completed you will need to restart Thunderbird.
Once installed you may be asked to Restart Thunderbird
Install Exchange EWS Provider Add-on for Lightning
The Exchange EWS Provider is an add-on for the Lightning Calendar. Enabling communication with Exchange 2007, 2010 and 2013 and Exchange online using the Exchange Web Service interface.
You can access any Calendar, Task, Contacts folder and Out of Office settings on the EWS server easily.
To install an additional plugin integrate your Calendar with Office 365.
Download and install Exchange EWS Provider Add-on for Lightning.
Exchange EWS Provider
Visit the GitHub page and right click on the link exchangcalendar-v{version number}.xpi and select Save Link As...
This will download the the plugin. To install the plugin go back to your Thunderbird Addon and click on Cog Icon and select Install Add-on From File
Navigate to folder to which you downloaded the file to and install the plugin. You may be asked to restart Thunderbird again.
Configure your Calendar
All the installation is now complete, all we now need to do is set up a calendar and you’ll be up and running. To do this you need to navigate File –> New –> Calendar,
This will open a new dialog, select On the Network and Next
Select Microsoft Exchange 2007/2010/2013 and Next
Give your Calendar a name and click next
Fill the Server URL: https://outlook.office365.com/ews/exchange.asmx or https://outlook.live.com/ews/exchange.asmx
Enter your email address for Office 365 and click Check Server and mailbox
Click Check server and mailbox
You should see an input dialog for your password, enter your password, and check the to save it. Clicking next will complete the process, and you should now have your Office 365 calendar set up on Thunderbird.
You should be able to Click Next and Finish.
Your calendar is now Available and you are able to do 2 way editing of your calendar appointments etc.
Conclusion
Once complete and configured you will now have complete two-way binding of all calendar appointments in your calendar.
Please note that the Exchange calendar plugin is an open source project, and is likely to change going forward, so readers should be aware and keep an eye on versions as and when the tool is updated. Also consider making a donation to the project to compensate the developers.
If you have any issues or found any variations in the process. Please let us know in the comments below and I will try to assist as much as we can.