Sync mailbox.org Calendar with Google Calendar or Microsoft 365

mailbox.org offers full-featured calendar and contact management alongside email — powered by Open-Xchange and the open CalDAV standard. The problem: if you use Google Calendar or Microsoft 365 at work, there's no way to connect your mailbox.org calendar directly. Google and Microsoft don't accept incoming CalDAV connections from external servers.

CalDAV works — but only in one direction

mailbox.org provides a full CalDAV interface. Calendar apps like Thunderbird, GNOME Calendar, or DAVx⁵ on Android can connect without any issues. But syncing with Google Calendar or Microsoft 365 fails because these services don't accept arbitrary CalDAV servers as a source.

Setting up an app password (required)

mailbox.org does not allow CalDAV authentication with your regular account password. You need to create a dedicated app password — regardless of whether you use two-factor authentication (2FA) or not.

How to create an app password:

1. Log in to the mailbox.org web interface
2. Go to Settings → Security → App Passwords
3. Create a new password with CalDAV/CardDAV permission
4. Copy the generated password — it's only shown once

Use this app password as your credentials in CalDAVconnect.

Your mailbox.org CalDAV URL

mailbox.org uses a central CalDAV endpoint:

https://dav.mailbox.org

CalDAVconnect automatically discovers available calendars via CalDAV Discovery — you don't need to enter a calendar-specific URL. If you have multiple calendars in your mailbox.org account (e.g. "Personal" and "Work"), all of them are listed for selection.

Bidirectional sync with CalDAVconnect

CalDAVconnect bridges your mailbox.org calendar with Google Calendar or Microsoft 365 — bidirectionally and within seconds.

How the sync works:

• Changes in Google Calendar or Microsoft 365 sync to mailbox.org within 1–2 seconds via webhooks
• Changes in mailbox.org sync to Google or Microsoft within 7–8 seconds on average via CTag polling
• No Outlook add-in or desktop client needed — everything runs in the cloud

Setup:

1. Create a CalDAVconnect account
2. Enter https://dav.mailbox.org as the CalDAV URL
3. Enter your mailbox.org email and app password as credentials
4. Connect your Google or Microsoft account via OAuth
5. Select calendar pairs and start syncing

Multiple calendars and custom domains

mailbox.org supports multiple calendars per account and custom domains. CalDAVconnect discovers all calendars via CalDAV Discovery — you can map each one to a specific Google or Microsoft calendar. Authentication always uses your mailbox.org email address, even with a custom domain.

Private Mode for sensitive events

CalDAVconnect's Private Mode lets you mark specific calendar pairs as private. Events are then synced as placeholders only — the original title, description, location, and participants remain hidden on the target calendar. This lets you see your availability at a glance without exposing confidential details.

Privacy

mailbox.org users choose their provider for a reason — privacy matters. CalDAVconnect is hosted on Hetzner infrastructure in Nuremberg, Germany. All data stays within the EU and is encrypted at rest. A Data Processing Agreement (DPA) pursuant to Art. 28 GDPR is available.

CalDAVconnect is currently in public beta and free to use. Join the beta and connect your mailbox.org calendar in minutes.