This feature is available in paying plans. To sync contacts and calendar events with Thunderbird, please use the TBSync add-on:

Works with Thunderbird version 91.0a1 – 91.*

1. Open Thunderbird client.
2. Install TBSync and Provider for Exchange ActiveSync add-ons.
3. Open the TBSync account manager by clicking on Tools -> Add-on Preferences -> TBSync.
4. Click on Add new account (at the bottom left) -> Exchange ActiveSync.
5. Select Server configuration: Custom configuration, and provide the following:
   Account name: Display name of your account.
   Username (email address) and Password
   Server address: www.mailfence.com
6. Click on Add account.
7. One done then open your TBSync account manager and check Enable and synchronize this account.
   1. Make sure to check both your calendar Events and Contacts listing populated under Available resources.
   2. Click on Synchronize now.

Note: TBSync does not support push sync. Therefore, changes will only be synchronized if you click on Synchronize now. However, you can enable AutoSync by settings up a sync interval in minutes. TbSync will then synchronize your account automatically.

If you are still unable to sync contacts and calendar events with Thunderbird, please contact support@mailfence.com (PGP key).