Sync Synology Calendar with Google Calendar or Microsoft 365

Synology NAS devices ship with Synology Calendar — a full-featured CalDAV calendar server. For teams and families who want to keep their data on their own hardware, it's an appealing choice. But how do you get those events into Google Calendar or Microsoft 365?

The challenge: Synology behind a router

Unlike cloud-hosted CalDAV servers (Nextcloud on a VPS, for example), a Synology DiskStation typically runs on your local network behind a router. That means:

No public access — the CalDAV server isn't reachable from the internet unless you set up port forwarding, DynDNS, and an SSL certificate
Security risk — exposing a NAS directly to the internet significantly increases the attack surface
Dynamic IP — residential internet connections frequently change IP addresses, breaking connectivity

Many Synology users rightfully hesitate to open their DiskStation to incoming connections.

QuickConnect and Synology Relay

Synology's QuickConnect feature allows access to the DiskStation without port forwarding. However, QuickConnect only works through the web browser and specific Synology apps — it doesn't support arbitrary CalDAV clients. For external sync, QuickConnect is not an option.

Reverse proxy as an alternative

Advanced users set up a reverse proxy (either on the Synology itself or an external VPS) to make the CalDAV server securely reachable. This works but requires technical knowledge for SSL certificates, DNS records, and proxy configuration.

If you go this route, the CalDAV URL for Synology Calendar is:

https://your-domain.com:5006

Port 5006 is the default HTTPS port for Synology Calendar. CalDAVconnect discovers available calendars automatically via CalDAV Discovery.

Bidirectional sync with CalDAVconnect

Once your Synology Calendar is reachable from the internet — whether through port forwarding, reverse proxy, or a VPN tunnel — CalDAVconnect connects it to Google Calendar or Microsoft 365.

How the sync works:

Changes in Google Calendar or Microsoft 365 sync to Synology within 1–2 seconds via webhooks
Changes in Synology Calendar sync to Google or Microsoft within 7–8 seconds on average via CTag polling
Multiple calendars per NAS are supported — each can be mapped to a different Google or Microsoft calendar

Setup:

Create a CalDAVconnect account
Enter your Synology CalDAV URL (e.g. https://your-domain.com:5006)
Enter your Synology username and password
Connect your Google or Microsoft account via OAuth
Select calendar pairs and start syncing

Synology-specific details

Synology Calendar uses its own CalDAV implementation — not Radicale, SOGo, or Open-Xchange. A few things worth knowing:

Recurring events: Synology fully supports recurring events, including exceptions (EXDATE) and modifications of individual occurrences
Invitations: Synology Calendar processes CalDAV invitations (iTIP), which is relevant for syncing with Google Calendar
Permissions: Make sure the user account you use for CalDAVconnect has read and write access to the desired calendars

Private Mode for shared NAS calendars

If you sync a shared family calendar from your Synology to Google Calendar but don't want all details visible: CalDAVconnect's Private Mode syncs events as placeholders only — title, description, and participants remain hidden on the target calendar.

Privacy

Your calendar data stays on your Synology DiskStation. CalDAVconnect only stores the sync metadata needed to keep things in sync — encrypted on Hetzner infrastructure in Nuremberg, Germany, within the EU.

CalDAVconnect is currently in public beta and free to use. Join the beta and connect your Synology Calendar with Google or Microsoft in minutes.