Set up CardDAV Connection in Apple Address Book

1. To add the mail.co.uk address book, open the "Contacts" app on your Mac and go to "Contacts / Preferences / Accounts".
2. To create a new account, click the "+" button.
3. In the following window, select "Other Contacts Account…".
4. Enter the following values in the form:
   Make sure to select CardDAV, not LDAP.
   Account Type: Automatic
   Username: your email address or custom login name if you have one
   Password: your mail.co.uk password
   Server address is now usually filled automatically. If entering manually, use:
   Server Address: https://adressbuch.mail.de:443/principals/max.mustermann@mail.de
5. Click "Sign In".
6. Your CardDAV account will now appear in the list.
7. When you exit the settings and open Apple Contacts, your mail.co.uk address book will be listed there.