Thunderbird is a feature-rich and mature mail client that can be turned into a full-fledged Personal Information Manager (PIM). Since version 102, it supports address book synchronization via CardDAV and automatic discovery of calendars and address books available on the server.
Looking to add a Nextcloud Talk meeting link to your invitations from Thunderbird? See Nextcloud Talk in Thunderbird (NC Connector).
Recommended method
Since Thunderbird 102, the CardDAV & CalDAV protocols are natively supported.
Contacts
On the address book view, click the down arrow near New Address Book and choose Add CardDAV Address Book.
In the next window, type your Username and Location (Server URL).
The next window will ask for your username and password for this account.
The previous window will be refreshed and ask you which address books you wish to sync.
Choose and then click Continue.
If you later want to add a new address book, you can redo all of those steps and only the books not already synchronized will be suggested.
If your account uses two-factor authentication, you need a dedicated app password for login rather than your regular password.
Calendars
Setting up a calendar takes two parts: first collect your connection details in Nextcloud, then add the calendar in Thunderbird.
Part 1 — In Nextcloud (collect your details)
Open the Calendar app, go to Calendar settings and copy the CalDAV URL.
Calendar settings — copy the CalDAV URL.
Go to Personal settings → Security → Create new app password. Enter a name (for example "thunderbird") and create the password.
Security settings — create a new app password.
Copy the generated login username and password. For security reasons the password is shown only once.
The login username and app password (shown once).
Part 2 — In Thunderbird (add the calendar)
Go to the calendar view and select New Calendar… at the bottom of the left side panel.
New Calendar… at the bottom of the calendar panel.
Choose On the network.
Select “On the network”.
Enter the Username (the login from Part 1, step 3) and the CalDAV URL as the Location, then click Find Calendars.
Enter the username and CalDAV URL, then Find Calendars.
Fill in the app password, choose which calendars you want to add, and click Subscribe.
Select the calendars and click Subscribe.
If you later want to add more calendars, just redo the procedure.
Alternative: Using the CardBook add-on (Contacts only)
CardBook is an advanced alternative to Thunderbird’s address book, which supports CardDAV.
Click the CardBook icon in the upper right corner of Thunderbird.
The CardBook icon in the Thunderbird toolbar.
In CardBook, go to Address book > New Address book > Remote > Next.
Select CardDAV and fill in the address of your Nextcloud server, your user name and password.
Select CardDAV and enter your server and credentials.
Click Validate, then Next, choose a name for the address book and click Next again.
Validate and name the address book.
When you are finished, CardBook synchronizes your address books. You can always trigger a synchronization manually by clicking Synchronize in the top left corner of CardBook.
Trigger a manual sync with the Synchronize button.