Synology Contacts Technical Specifications

A centralized web-based interface for managing contacts of CardDAV-compatible clients
Custom fields for contact creation, modification, and search
Contact categorization with labels and address books that can be shared with Synology NAS users
Integration with Synology MailPlus to suggest contacts for email recipients

Supports syncing contacts to mobile devices or laptops via CardDAV
Supports syncing or importing address books from Google, Microsoft Outlook, and third-party CardDAV servers upon login
Supports importing address books from a vCard (.vcf) or Google CSV file and exporting address books to a vCard (.vcf) file
Supports managing and filtering contacts with labels and stars
Provides three types of address books:
- Personal address book: The default address book for individual users, including suggested and starred contacts
- Shared address book: The address books that other users share with you
- Group address book: The default address book based on the Synology Contacts binding account system
Provides fields for editing and search, including name, company, department, job title, email, phone number, address, website, birthday, event date, chat app, and note
Serves as a contact management add-on for Synology MailPlus when they are installed on the same Synology NAS

Only one-way sync from external sources to Synology Contacts is supported. Any changes made in Synology Contacts will not be updated to the source address books