Cardbook for Thunderbird is an add-on that allows to manage all your contacts
under the CardDAV standard. It is developed by Philippe Vigneau.
By sticking strictly to the VCARD standard (in its most current versions), functionality of the service is assured for a large variety of server platforms, including Google. Syncing contacts between Thunderbird and any CardDAV-enabled device has never been more comfortable! This add-on enables an easy access to contacts anywhere.
The add-on features a large number of very useful functions, like customizable data fields, Phone number validation and unlimited categories, email addresses, phone numbers, addresses, chat programs, URLs, calendar events per contact. And much more. Managing your contacts becomes a breeze!
The purpose of this website is to offer a forum for exchange with the developer.
A Wiki has been started here – this is work in progress and contributions are welcome.
Troubleshooting starting page : https://cardbook.icu/forum/troubleshooting/