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There is no direct way to synchronize calendars between the Outlook client and other applications. You need to export your Outlook calendar before importing it to other software. However, exporting calendars from a browser client is more complicated, so follow these steps to export calendars:
- Log into your Outlook account.
- Click on the gear icon in the upper right corner and select View All Outlook Settings.
- Navigate to Calendar > Shared Calendar.
- Under Publish a Calendar, select your calendar and choose to publish it. This will generate an ICS link.
- Use the ICS link to download your calendar events locally.
Then import your calendar from the Thunderbird side.
Exporting calendars from the desktop client is easier than a browser client. At the top of the ribbon in classic Outlook, choose File. Choose Open & Export > Import/Export. For more details, you can see: Import and export Outlook email, contacts, and calendar.
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