Both Nextcloud and Owncloud work very well as cardDAV servers with CardBook.
Note: only 1 address book per userID is possible (restriction by Nextcloud/Owncloud).
Configure CardBook with this URL: https://youraddress.tld/remote.php/dav/addressbooks/users/YourUsername/contacts/
Thunderbird does not natively support CardDAV synchronisation. You will need to install a third party adapter to use CardDAV, such as CardBook.
Be aware that any pre-existing contacts already on your device do not automatically get copied back up to FastMail with the sync: you need to import them to FastMail first.
Install the Thunderbird Add-On "Cardbook" through Thunderbird's add-on manager.
Click on "Cardbook" in the Thunderbird menu bar
Select "Add addressbook" and then "Remote"
Continue and choose "CardDAV"
Username: Your FastMail email address
Password: Create a new
app password with CalDAV access in the FastMail
web interface. Use this app password for CardBook.
If you are a member of a multi-user (business) account, you will have shared
contacts as well as personal contacts.
You can choose to sync one or both. Choose your contact list colours and leave
the vCard setting as 3.0.
CardBook works with the popular Synology NAS devices. (Some users however report degraded sync performance with >300 contacts.)
Install the CardDav Server App from the package center. There is not much to configure in the app: You can only chose what ports to use and whether to activate https (and if so, if requests are automatically forwarded to https).
1. Configuration with http
Let's assume you use http with port 8008.
First, on your router you need to set up port-forwarding of port 8008 to your NAS. (Specific instructions for this depend of your router model and shouldn't be difficult to find on the Net.)
Then configure CardBook with this URL: http://yourddns.tld:8008/addressbooks/users/YourUsername/addressbook/
2. Configuration with https and Let's Encrypt certificate
For https forward port 8443 of your router to the Synology.
Note: The connection via https will fail if there is only a self-signed certificate for the domain (as is the default). Therefore you will need a recognised certificate.
Since DSM 6 it is possible to install a free certificate from Let's Encrypt on the Synology NAS. The process is quite straight-forward. Installation of a Let's Encrypt certificate requires forwarding of port 80 to the Synology. Here are good tutorials: 🇬🇧🇫🇷🇩🇪
If you have >1 certificate installed on your Synology, make sure to select the right one for the CardDav Server app by clicking on Configure on the Certificates page of your Synology and adjust as necessary. Make sure to configure CardBook with the address corresponding to your certificate, or the connection will fail.
Configure CardBook with this URL: https://yourddns.tld:8443/addressbooks/users/YourUsername/addressbook/