CalDAVconnect
Log in Join the beta
Home Blog Pricing Docs
Log in Join beta
← Back to blog

Sync SOGo Calendar with Microsoft 365 and Outlook

· 4 min read
SOGo Microsoft 365 Outlook CalDAV ActiveSync

SOGo is one of the most popular open-source groupware solutions, especially in enterprise environments. But connecting SOGo calendars with Microsoft 365 has always been challenging. Let's break down the options and why most of them fall short.

The current state of SOGo + Microsoft integration

SOGo offers several ways to interact with Microsoft products, but each comes with significant limitations:

ActiveSync (SOGo Connector)

SOGo supports Microsoft's ActiveSync protocol, which allows Outlook Desktop and mobile devices to sync calendars, contacts, and emails. However:

  • ActiveSync syncs with the local Outlook client, not with Microsoft 365 cloud calendars
  • Events synced via ActiveSync are stored locally in Outlook — they don't appear in your Microsoft 365 cloud calendar
  • If you switch devices, you need to set up ActiveSync again
  • The new Outlook (2024) has limited ActiveSync support and behaves differently from Outlook Desktop

Outlook CalDAV Synchronizer

SOGo's website recommends the Outlook CalDAV Synchronizer for connecting SOGo calendars with Outlook. This was a solid solution — until Microsoft released the new Outlook in 2024.

The Outlook CalDAV Synchronizer is a COM Add-in, and the new Outlook does not support COM Add-ins. For users who have migrated to the new Outlook, this tool is no longer an option.

ICS feed subscriptions

You can subscribe to a SOGo calendar's ICS feed from Microsoft 365. But as with any ICS subscription:

  • It's read-only — you can't edit events
  • Microsoft 365 refreshes feeds on its own schedule (often 24+ hours)
  • There's no bidirectional sync

Understanding the difference: Outlook Desktop vs. Microsoft 365 Cloud

This distinction is crucial and often causes confusion:

Outlook Desktop is a native Windows application that stores calendar data locally. It can sync with Exchange/Microsoft 365 servers, but it can also maintain local-only calendars. ActiveSync and COM Add-ins work with Outlook Desktop.

Microsoft 365 (cloud) is the server-side calendar that's accessible from:

  • Outlook Web Access (outlook.office.com)
  • The new Outlook for Windows
  • Outlook for Mac
  • Outlook mobile apps
  • Any third-party app using the Microsoft Graph API

When most people say they want "Outlook sync," what they actually need is Microsoft 365 cloud calendar sync — because that's what makes events available on all their devices.

The solution: CalDAVconnect

CalDAVconnect syncs your SOGo calendar directly with your Microsoft 365 cloud calendar via the Microsoft Graph API. This means:

  • Events appear in the new Outlook, Outlook Desktop, Outlook Web, and Outlook mobile
  • No client-side software or add-ins required
  • Real-time sync via webhooks — not periodic polling
  • Bidirectional — create events on either side

How it works

  1. CalDAVconnect connects to your SOGo server via CalDAV
  2. It connects to your Microsoft 365 account via OAuth (Microsoft Graph API)
  3. Calendar changes are synced bidirectionally in real-time

Because the sync happens at the cloud level, it works regardless of which client you use to access your calendars.

SOGo → Microsoft 365 sync flow

SOGo Server ←(CalDAV)→ CalDAVconnect ←(Graph API)→ Microsoft 365
                                                        ↓
                                               New Outlook
                                               Outlook Desktop
                                               Outlook Web
                                               Outlook Mobile
                                               Teams

Getting started with SOGo + Microsoft 365

  1. Sign up for CalDAVconnect (free during the public beta)
  2. Add your SOGo server:
    • CalDAV URL (typically https://your-sogo-server/SOGo/dav/username/Calendar/personal/)
    • Your SOGo credentials
  3. Connect your Microsoft 365 account via OAuth
  4. Select the calendars to sync
  5. Initial sync runs automatically

The entire process takes about 5 minutes. After that, changes sync in real-time.

For SOGo administrators

If you manage a SOGo installation for your organization, CalDAVconnect can help your users who need Microsoft 365 integration:

  • No server-side changes required — CalDAVconnect connects as a regular CalDAV client
  • Per-user setup — each user connects their own accounts
  • No ActiveSync configuration needed for Microsoft 365 sync
  • Works alongside existing ActiveSync — users can use both if needed

Privacy and compliance

CalDAVconnect is hosted on Hetzner in Nuremberg, Germany. Your calendar data is processed exclusively within the EU. All event data is encrypted at rest. CalDAVconnect is fully GDPR compliant .

This makes CalDAVconnect suitable for organizations with strict data sovereignty requirements, which is often the reason they chose SOGo in the first place.

Conclusion

The combination of the new Outlook dropping COM Add-in support and the limitations of ActiveSync for cloud calendar sync has left many SOGo users without a good option. CalDAVconnect provides a modern, cloud-based bridge between SOGo and Microsoft 365 that works with every Outlook version and syncs in real-time.