Should you run the CDO update before or after rebasing?
Published Jan 08 2019 01:23 PM 277 Views
First published on TECHNET on Feb 28, 2007

Q: Should you run the CDO update before or after rebasing?  We are getting conflicting inputs

A: The current recommendation is to run the server side CDO update and then rebase. But you shoudl know that OWA-created recurring items will not be rebased if this order followed. If there are recurring calendar appointments that were scheduled through OWA, putting on the CDO patch first will prevent these from being rebased.  This is why we recommend applying KB 926666 ("Update for daylight saving time changes in 2007 for Exchange 2003 Service Pack 2" the CDO update, ) after rebasing in OWA-heavy environments.

More details: Microsoft calendar software such as Outlook depends on the operating system time zone information to display time information. However, Collaboration Data Objects (CDO)-based programs such as Outlook Web Access depend on separate internal time zone tables. This update modifies these internal time zone tables to match the changes in time zone settings. Without this update, calendar items in CDO-based programs and in Outlook Web Access will operate as if standard time is in effect during the extra weeks of daylight saving time. For example, without this update CDO-based programs will operate in standard time during the following periods in 2007 which we refer to as the extended DST period:

• March 11, 2007 through April 1, 2007
• October 28, 2007 through November 4, 2007

General Installation Order Guidance: Because many calendar environments have an interconnected system of applications, each environment must be adjusted to accommodate the new DST rules. Please refer to for more information and the general sequence of update actions and special considerations

Generally, we recommend the following sequence of DST update actions:

  1. Apply updates to Windows operating systems on Windows Servers. ( KB 931836 )

  2. Apply updates to Windows operating systems on individual workstations. (also KB 931836 )

  3. Apply the Exchange Server DST update. (aka DST update for CDO, KB 926666 )

  4. Rebase calendar appointments (using TZMove KB 931667 / TZMove update KB 933146 / Exchange tool KB 930879 )

Recommended order when users create recurring calendar items in OWA: Perform step 4 (Rebase) before step 3  (Apply Exchange CDO update).  If OWA is not used in the environment, then rebasing can be performed before or after installing the Exchange update for CDO.

In step 4 above, the IT administrator has one of four alternatives depending upon their (pros and cons of each alternative are described):

  • Run the Exchange Calendar Update tool against all affected users, servers, or both.

  • Push out the Outlook Time Zone Data Update tool to the clients and let the users update their own mailboxes.

  • Run the Exchange Calendar Update tool against all affected users, servers, or both, but only modify recurring appointments. Then ask users to rebook single instance appointments that fall into the extended DST period or ask them to run the Outlook Time Zone Data Update tool. Or

  • Run neither the Exchange Calendar Update tool nor the Outlook Time Zone Data Update tool. Ask users to examine their calendars and rebook as necessary.

IT administrators are strongly advised to refer to the Exchange Calendar Update tool KB article 930873 ( ) and consider all potential effects on their IT environments and user base of those alternatives before running the Exchange Calendar Update tool.

(Revised 030307: Added detail on CDO impact, added general update installation guidance)

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