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Comprehensive Guide on Addressing Exchange Calendaring Issues

Lost Appointments, Duplicate Appointments, Odd Delegate Issues, etc

This is a follow-on to a blog post I did the other day titled "Comprehensive Guide on Addressing Slow / Sluggish Outlook Performance to Microsoft Exchange" posted at  I am continuing that post here specifically focused on Calendaring issues in Microsoft Exchange. (note: this blog post has been repeatedly updated with current information, latest update, March 28, 2011  (note: I created a 2014 Update to this posting at

Beyond the previous post of general complaints of slowness and sluggishness in Outlook and Exchange, the other complaint I hear frequently these days is specific to Calendaring.  Part of it is calendaring performance (where it might take 20-30 seconds to open up somebody else's calendar to view their calendar) which all of the points I note in the other blog post referenced above will apply to performance issues in calendaring.

In this post, I'm going to address other areas specific to calendaring such as:

  • Lost Appointments: Appointments sent to someone, the person accepted the appointment, but now the appointment isn't in their calendar anymore
  • Duplicate Appointments:  Having the same appointment show up multiple times in the calendar
  • Appointment Corruption:  Appointments (typically recurring appointments) that cannot be opened as an error notes "Cannot read one instance of this recurring appointment.  Close any open appointments and try again, or recreate the appointment"
  • Odd Delegate Issues:  Where a Boss/Delegate relationship is challenged by the delegate not getting appointments consistently, or approvals not showing up as approved

If users in your organization are having problems with calendaring in Exchange, you aren't alone, the problem does exist and it's not 100% "user error" where a user is deleting appointments and not knowing it, or a user is screwing up their calendar (at least not 100% of the time, maybe 20-30% of the time), but more frequently it is quirks in Exchange / Outlook / Add-ins that cause the user to do something that causes the appointments to get screwed up.

The following content is not based on my opinion or speculation, but rather proven experiences backed by direct links to Microsoft, Apple, Blackberry, and other main source resources that point to specific problems in Exchange calendaring.  What I have added is the technical background (ie: why the problems exist) hopefully in clear English so you understand how the problems have come to be, and what you can do things to fix the problems.  I have worked with hundreds of companies (small 100 person to large >100,000 person orgs) where calendar problems have been fixed and are no longer an issue, so the problem is solvable.

Here are the big picture issues...

Apple Mac / Windows Mixed Environments

One of the biggest causes of calendar issues in Exchange occurs in environments that have mixed Apple Mac and Microsoft Windows systems in their environment, and moreso when the Manager/Assistant relationship crosses system type boundaries (ie: Manager has Mac, Assistant has Windows).  Some of the specific problems, prior to Entourage 2008 Web Services Edition (WSE) that came out as an update to Entourage 2008 in the Summer of 2009, Entourage 2008 (and Entourage 2004) did not support attachments in calendar appointments  When a Window user sends an appointment with an attachment, Entourage 2008, Entourage 2004, Mac Mail client prior to Mac OS 10.5 would delete the attachment and save the appointment without the attachment. 

This in effect "changed" the appointment so that now you have an appointment with an attachment (for Windows users) and an appointment without the attachment (for Mac users).  If a Mac user now changes the appointment and sends an update, it is effectively sending a completely different appointment request (the version of the appointment without the attachment).  Mac users will see 1 copy of the appointment, Windows users will typically see 2 copies of the appointment (one with, and one without the attachment).  And note, people who put little graphics in their address footer are effectively putting attachments into a calendar appointment, so it doesn't need to be a Word doc attachment, it could be simply a company logo, "go green" logo, or other graphic slipped into their address/signature block that is an attachment that creates an error between Mac and Windows users.

Prior to Entourage 2008, the Mac did not support access to Exchange 2007 (or higher) free/busy information which is a key component in checking for appointment conflicts or meeting status information.  There are common problems for users in an Exchange environment running Entourage 2004 that corrupt calendar information because of the lack of free/busy information access.

Solution:  In an environment with both Windows and Mac clients, it is HIGHLY recommended that the Mac users use the latest client to Exchange as possible at a minimum Entourage 2008 Web Services Edition (WSE) with the latest patch/update level, or (as of this update 3/2011) to Office 2011 for Mac (which has proven to greatly improve compatibility between Macs and Windows systems).  Other options include the Mac MailApp in Mac OS 10.6 or higher.

For Manager/Assistant relationships, it is HIGHLY recommended (or if I can clarify, a requirement) that the same version of operating system and mail client is used, so Windows/Windows, Mac/Mac, Office 2007/Office 2007, Office 2010/Office 2010, or the like.  When you mix platforms and versions of mail client, because attribute storage and management are different across platforms and across versions of the mail client, when a shared relationship exists where an individual is frequently accessing, modifying, editing another person's calendar, more problems in calendaring exist.  Keep to the same platform and mail application.  In many environments where an Executive Assistant is the assistant for multiple individuals where some individuals have Windows and some have Macs, the situation gets more complicated. 

In these scenarios, the key is to identify who has WRITE capabilities to calendars.  If all appointments are sent by the assistant running Windows, and the Mac user (the executive) is only a recipient of meeting appointments, then the problems are minimized.  The problems exist when the assistant sends out a meeting request, and the executive (also with write and meeting creation capabilities) changes the meeting so effectively the meeting is sent/written/edited/updated cross platform.  This is when meeting corruption happens most frequently.  We have been advising organizations with cross-platform executive/assistant models that have multiple platforms to consider providing the assistant both a Windows computer and a Mac computer on their desk to handle meeting requests on different systems using the same platform as the executive to ensure calendar integrity.  In ALL situations where we've had organizations implement dual platforms for the assistant, the calendar corruption problems related to this cross-platform situation have completely gone away. (note: this could be a Mac computer with a virtualized Windows guest session (running Parallels or VMware Fusion) to get dual platforms on a single system.

Technical Background:  To answer "why" this happens, the focal point is delegation of calendaring.  As a delegate, the individual has 100% read/write access to the exact same information as the owner of the content.  Effectively you have TWO (or more) individuals that have full read/write/edit capabilities to content.  Think about opening up a Microsoft Word doc at the same time with 2 or more people (which is a feature Microsoft has forbidden until just recently with Office 2010), the reason opening up the same Word doc at the same time has been forbidden in the past is to prevent file corruption.  Unfortunately Exchange does provide simultatneous access to calendars so that 2 or more individuals can have a calendar appointment open at the same time. 

Think then, what happens if one individual has the calendar appointment open on Windows that has full attribute access to the appointment, and at the exact same time another individual opens that same calendar appointment but their client software automatically deletes any attachments because that version of the client software deletes attachments (ie: Entourage 2008 or earlier).  When the two individuals "save" the calendar, which version of the calendar appointment is saved?  The answer, sometimes both (creating duplicate calendar appointments), sometimes one version (which might include a time/date change), sometimes the other verison (which might not include a time/date change), or sometimes both copies of the appointment are deleted (thus having the appointment "disappear" from the user's calendar).

I always get asked, why would the appointment up and disappear?  The answer:  Have you ever been invited to a meeting, then the sender changes the meeting appointment and sends you an update before you even accepted the original invite, and if you are using Outlook 2007 or 2010, the first meeting appointment ends up in your Deleted Items folder, and the updated appointment is now in your inbox for you to accept (so it already deleted the first meeting request and replaced it with a second meeting request)?  That behavior was built in to Outlook 2007 (and 2010) so that you only see 1 copy (the most current copy) of the invite.  And if you accepted the first invite, then the 2nd request shows up as "No Response Required" basically just a notification.  However, that experience was different with Outlook 2003 (and Entourage, Office 2011 Mac, and most importantly for iPhone/iPads). 

The earlier experience would be you see the first invite AND you see the 2nd invite both with Accept/Decline options.  Here's where the mixed version problem comes in to play.  If you have a manager running Outlook 2003 and a delegate using Outlook 2007 (or Mac Entourage and Outlook 2007, or Outlook 2003 and Outlook 2010, iPhone/Ipad, etc), with 2 people with the same meeting open and being viewed, the Outlook 2003/Entourage/iPhone/iPad user can be viewing the meeting (but not accept it yet) and the meeting change comes along with a "No Response Required" to the Outlook 2007 delegate, the Outlook 2003/Entourage/iPhone/iPad user can close the appointment without accepting it, the 2nd request is ignored because it had a "No Response Required" flag, and the entire appointment would be ignored and not entered into the person's calendar because neither the executive nor the delegate actually accepted the invite.

Compound this issue, as of this February 2011 update, there is a known bug in the Apple iOS that further complicates this timing issue.  Here are some issues (with confirmed repro steps) that we've identified and have investigated for root cause and fix. Bugs are open on both sides (MSFT & AAPL).  The known issue: If an organizer sends a request to manager with a delegate, manager’s delegate accepts invite via Outlook, organizer changes a single occurrence of the meeting, manager declines the single occurrence from an iOS device. As a result whole series is removed from manager’s calendar.

Another set of repro steps: Organizer sends a request to an attendee, attendee accepts the invite via Outlook, attendee then leaves his desk, organizer changes a single occurrence of the meeting, attendee declines the single occurrence from an iOS device while away from his desk. As a result the entire meeting series is removed from attendee’s calendar.

This all can happen when you have multiple invites in your Inbox and respond to latest updates (single or multiple occurrences) first before acting on original invite (series). This usually happens when a manager is set to receive copies of all meeting related messages. Its recommended to not set that, especially for users using iOS devices or educate users on interaction with meetings on their iOS devices. Outlook (2007/2010) addresses that by sending an informational update to manager, iOS does not do that currently as related property is in the Exchange ActiveSync v14.1 (default in Exchange 2010 and prior), which the property is not implemented in iOS yet.

Another reported issue is where the meeting attendee list is altered and its cascade impact on the actual meeting invite.

So this problem does not have to be Mac/Windows as the issue of calendar problems, an Outlook 2003 / Outlook 2007 (Windows/Windows) / iPhone-iPad Manager/Assistant relationship configuration can have the same affect due to underlying bugs in the iPhone/iPad iOS.

Solution to the iPhone/iPad problem is to keep the devices up to date on the latest versions of the updates, preferrably using a centralized device management tool like JAMF Casper, Microsoft System Center 2007 with iPhone/iPad 3rd party plug-ins, or Microsoft System Center Configuration Manager 2012 (currently in beta) with native mobile device management support.

There are variations to this where Blackberry, iPhones, and other full access devices also change the attributes of the appointment rendering changes to the appointment that cause the appointment to never end up (or automatically removed) from a person's calendar.  More details below.

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