KAddressBook stores all the personal details of your family, friends and other contacts. It supports large variety of services, including NextCloud, Kolab, Google Contacts, Microsoft Exchange (EWS) or any standard CalDAV server.
Connect to an external service?
- Synchronizing NextCloud with KDE PIM (NextCloud Documentation)
Backing up your Data
The page Akonadi and AddressBook helps you understand the structure of KAddressBook, so that you can be sure that you have backed up all that you need.