---
title: "Email Encyclopedia: What is CardDAV"
date: 2025-07-18
artist: Yuanshu
summary: "CardDAV is an open contact synchronization protocol that supports multi-device contact synchronization and sharing, with cross-platform compatibility and high security, widely used in both personal and enterprise scenarios."
tags: ["Email Encyclopedia", "Alibaba Mail"]
keywords: ["CardDAV, vCard, WebDAV, Contact Synchronization, Address Book, RFC 6352, Cross-platform Compatibility, Shared Address Book, HTTPS, Open Source Projects"]
description: "CardDAV is an open contact synchronization protocol that supports multi-device contact synchronization and sharing, with cross-platform compatibility and high security, widely used in both personal and enterprise scenarios."
---
**CardDAV** (vCard Extensions to Web Distributed Authoring and Versioning) is an internet standard address book synchronization protocol that allows users to synchronize contact information across multiple devices and applications over a network. As an extension of the WebDAV protocol, CardDAV aims to provide an open, standardized way to manage personal and shared address book data.
CardDAV was defined by the Internet Engineering Task Force (IETF) and officially published in 2010 as RFC 6352. The protocol is based on existing HTTP/HTTPS protocols, making it easy to integrate into modern internet architecture. It is widely used in email clients, calendar applications, and cloud service providers, with platforms such as Apple iCloud, Google Gmail, and Nextcloud all supporting the CardDAV protocol.
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## Historical Background
With the development of mobile devices and cloud services, users needed a way to access and update contacts on different devices. Early solutions were mostly proprietary protocols, resulting in poor interoperability between systems.
To address this issue, the IETF began developing the CardDAV protocol in 2003, with the goal of creating an open standard that would allow address book data to be seamlessly synchronized between different servers and clients. The protocol borrowed design concepts from CalDAV (the standard protocol for calendar synchronization) and incorporated the data structure of the vCard format.
In August 2010, RFC 6352 was officially published, marking CardDAV as an international standard.
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## Technical Principles
### Core Concepts
- **vCard**: CardDAV uses vCard (also known as vCard MIME type) as the data format for contacts. vCard is a universal electronic business card format that can store information such as names, phone numbers, email addresses, birthdays, and more.
- **WebDAV**: CardDAV is built on top of WebDAV, utilizing its file locking, version control, and namespace management functions to implement CRUD operations on contact data.
- **HTTP Methods**: CardDAV relies on HTTP/1.1 protocol methods, including GET, PUT, DELETE, PROPFIND, REPORT, etc., for interaction with the server.
- **Address Book Collection**: CardDAV organizes contacts into "address book collections," with each collection containing multiple vCard objects.
### Data Model
The core data unit in CardDAV is a vCard object, typically stored as a `.vcf` file. These objects can be added to address book collections and accessed and modified through HTTP requests.
The address book collection itself is a WebDAV collection resource with the following characteristics:
- Collection properties can be queried using the PROPFIND method;
- New collections can be created using the MKCOL method;
- Each vCard object can be accessed via a unique URL.
### Synchronization Mechanism
CardDAV supports incremental synchronization functionality, where clients can use the `sync-token` mechanism to retrieve changes since the last synchronization. This greatly improves synchronization efficiency, especially when handling large numbers of contacts.
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## Features
### Multi-device Synchronization
CardDAV supports synchronizing contact data across multiple devices. For example, users can use the same address book on smartphones, tablets, and desktop computers, ensuring consistent contact information across all devices.
### Shared Address Books
In addition to personal address books, CardDAV also supports shared address book functionality. Users can set address books with read-only or editable permissions, allowing multiple users to collaboratively maintain a group of contacts.
### Cross-platform Compatibility
Because CardDAV is based on open standard protocols, it can be used in a variety of operating systems and applications. Whether on Windows, macOS, Linux, or mobile platforms (iOS, Android), clients supporting CardDAV can be found.
### Security
CardDAV typically communicates via HTTPS protocol, ensuring data security during transmission. Additionally, servers can implement authentication (such as Basic Auth, OAuth) and access control policies to protect users' private data.
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## Application Scenarios
### Personal Users
For ordinary users, CardDAV can be used to synchronize contacts from one device to another. For example:
- After adding a new contact on an iPhone, the contact automatically appears in the "Contacts" application on a Mac computer;
- Users of the Thunderbird email client can connect to remote servers via CardDAV to achieve cross-device contact synchronization.
### Enterprise Users
In enterprise environments, CardDAV can be used to build a unified address book management system:
- Employees can access company-shared address books to find colleagues' contact information;
- IT departments can centrally manage contact data and distribute it to all employee devices via the CardDAV protocol;
- Integration with other systems (such as CRM, ERP) to achieve automated contact synchronization.
### Open Source Projects
Many open source software and services support the CardDAV protocol, for example:
- **Nextcloud**: A popular self-hosted cloud service platform that supports contact synchronization via CardDAV;
- **ownCloud**: Similar to Nextcloud, providing similar synchronization functions;
- **Radicale**: A lightweight CalDAV/CardDAV server suitable for small teams and personal use.