From Zimbra :: Wiki
Note: This info applies to Outlook profiles using the ZCS Connector for Outlook.
Using Outlook to access Free/Busy information from the Zimbra server
The Zimbra Connector for Outlook (ZCO) will automatically configure the Internet Free/Busy URL so Outlook can query the Zimbra Collaboration Server to obtain free/busy information for users. In certain cases you will want to override the url set by ZCO. Do to so:
Configure the following registry key to tell ZCO to not automatically set the free/busy url
Outlook -> Tools menu -> Options -> Calendar Options button -> Free/Busy Options button
If the hostname of your Zimbra server is domain.com, set the "Search Location" URL to the following (leaving %name%@%server% as the literal words "name" and "server" so that it will work for any account on the zimbra server):
Note: Starting with 5.0.7, the auth token is also required, and the above URL is no longer valid. You should let Outlook set the URL automatically. See http://bugzilla.zimbra.com/show_bug.cgi?id=28435 for details.
Accessing Free/Busy information over SSL
Note that this will silently fail if you are using https without a valid ssl certificate on the server. It should be possible to cause Outlook to trust the self-signed CA cert from the Zimbra server by importing it into Outlook with this guide from Microsoft though there may be complications due to varying certificate formats.
You may find these steps easier than the ones provided in the link above:
1. Open up Internet Exploror, preferably version 7 (run Windows Update to get it, if you don't have IE 7 already). 2. Navigate to https://webmail.yourdomain.com - Ignore any warnings about the site's certificates, and continue through to the Zimbra Web Client login page. 3. Click on the 'Certificate Error' alert next to the Address Bar. 4. Click on 'View Certificates'. 5. In the 'Certificate' window that appears, click on the 'Certification Path' tab. 6. Select the topmost certificate, 'Zimbra Collaboration Suite'. 7. Click the 'View Certificate' button. 8. From the 2nd 'Certificate' window that appears, click the 'Install Certificate' button. 9. Now follow the steps through the 'Certificate Import Wizard' by clicking the 'Next' buttons, accepting all defaults. 10. Click 'Yes' on the 'Security Warning' dialog that pops up when the wizard is finished. 11. All done! Close any remaining windows, close Internet Explorer, and restart Outlook. You should now be able to see people's free/busy status in the Outlook Calendar scheduler.
Giulio Harding: m.Net Corporation