Outlook Calendaring Issues with BPOS (Office 365)

The other day I got a Microsoft BPOS/Outlook issue (NOTE: BPOS is now called Office 365). Certain, heavy calendar users were experiencing a lot of issues. Here were the primary items:

  • Lag when switching between Delegated calendars/ inboxes etc.
  • Appointments not updating correctly.
  • Message interface error when switching between calendars
  • New event on calendar, no details shown
  • Duplicate entries on Calendar
  • Unable to determine who’s calendar you are viewing when using “calendar in Mail” view. The name was not listed on the tab.

Most of the problems occur because Outlook is not configured to work over a slower than usual connection. BPOS uses a login client that then connects to the “cloud” servers run by Microsoft. When running Exchange server on premises, you can rely on your 100MB network connection and not worry about bottlenecks occurring for certain heavy network operations. However, when using the advanced calendaring features of Outlook, it can put a strain on your ISP connection (upload/download is usually far less than 100MB). The core of the solution is outlined in this support article:


What you need to do is turn on the option to Cache Others Mail. This is not enabled by default and you should NOT set this for all users, JUST your heavy shared calendar users (like Administrative Assistants):

  1. Exit Outlook 2007.
  2. Start Registry Editor: Click Start, click Run, type regedit in the Open box, and then click OK.
  3. Locate and then click to select the following registry key:  HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Cached Mode, or you can use: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\Cached Mode
  4. Right-click CacheOthersMail, and then click Modify.
  5. Type 1 in the Value data box, and then click OK.
  6. On the File menu, click Exit to exit Registry Editor.
  7. Next, disable headers. To do this, follow these steps:
  8. On the File menu, and then click Cached Exchange Mode.
  9. Click to clear the following options:
    • Download Headers and then Full Item
    • Download Headers
    • On Slow Connections Download Only Headers

Additionally, the following article is a set of best practices for managing calendars. Some of the issues, like duplicates or cancellations not being accepted are likely due to appointments being modified, changed or the original e-mail request being moved, etc. The following article is an excellent resource to make sure appointments are handled properly to avoid issues:


This article describes the following scenarios in which Calendar items may be removed from the Calendar:

  • Multiple users receive meeting requests for a mailbox owner.
  • You delete a meeting request on one computer after you accept the same meeting request on another computer.
  • You cancel or delete a meeting without sending an update.
  • You frequently change recurring meetings.

This article also describes the following scenarios in which the Calendar items may become out of date:

  • You forward a meeting request.
  • You use Outlook Web Access to accept a meeting.
  • You do not click "Send Update" when you change a meeting that you organize.
  • You do not process a meeting request in the Inbox.

Finally, this article recommends the following best practices for working with meeting information:

  • Convert an existing appointment to a meeting request.
  • Do not forward meeting requests if you are not the meeting organizer.
  • Limit the number of delegates who have access to your Calendar.
  • Schedule end dates on recurring meetings.
  • Turn on Calendar logging for executives and for other frequent users.

Additional issues you may be having can be resolved by installing the latest set of patches called Cumulative Updates for Outlook and Office core (mso). The following website has a link to all of these patches:

Update Center for Microsoft Office, Office Servers, and Related Products


2 thoughts on “Outlook Calendaring Issues with BPOS (Office 365)”

  1. Great Article, but what about Outlook 2003? I know it works for 07 and 2010 but is it supported on Outlook 2003?

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