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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.

Blackberry Enterprise Server (BES)

I noted problems with Blackberry devices and services in their impact on Exchange performance in my previously posted article, the problem with BES is a huge source of problems for calendaring as well.  The problem with BES is that it was designed to act as a user's Outlook, listen/look for changes in emails and calendar appointments, and automatically forward the changes to the Research in Motion (RIM) network to a Blackberry device, a great solution built 10+ years ago when only a handful of executives and salespeople in an org had Blackberries, and people sent "a couple dozen emails" in a day.  But this process has gone effectively unchanged, and roll forward a decade when organizations now have hundreds of Blackberry devices managing users who are sending/receiving dozens/hundreds of emails in a day, the BES server using MAPI communications just can't keep up (note: RIM/Blackberry will be changing the architecture of their BES server in a major upcoming release to use secured Exchange Web Services that will address these problems and concerns, however for now, we're stuck with BES and MAPI, a highly inefficient and insecure method of communications).

Note:  My reference to "insecure" is the fact that BES uses a single "administrator" password to access ALL mailboxes of users with Blackberry devices and this security hole has been used to breach the security of Blackberry user accounts because anyone in IT can use the BES administrator account to effectively open and read anyone's mailbox with absolutely no security audit trail to determine who accessed an individual's mail.  But this is a separate topic to address.

Specific to calendaring problems, BES is well known to take on the load of what appears to be 4 users for every Blackberry device on the network ( and puts significant load on a single server against Exchange.  During peak times, Blackberry servers with as few as 500 devices connected to it can exceed the I/O capability of Exchange causing messages to be delayed by 5-10 minutes as they are queued up on the Blackberry server and in Exchange.  This delay easily reachs 10-15 minutes during a migration when an organization has some mailboxes on say Exchange 2003 or Exchange 2007, and other mailboxes on Exchange 2010 as the overtaxed Blackberry server now has to cross the Exchange boundary between server types to check on messages, route messages, validate messages, etc.

This delay time is not the problem, it's what happens "during" the delay that is typically human related that ties into my first bullet on Exchange calendaring across platforms (Outlook 2003 / 2007 / 2010, Apple Mac and Windows, iPhones/iPads, etc).  As a scenario, a desktop user sends a meeting request to several users, of which desktop recipients immediately get the meeting request and accept the request.  The Blackberry user, due to the delay in sending and receiving during peak times across a migration boundary has delays in their receipt of the meeting request, requests a change in the meeting, and sends a reply that might not get back to the originator for 5-15 minutes.  By then others have accepted the request while the change occurs, which a desktop user might request a different change which now the Blackberry user is 2 request changes behind. 

The timing factor causes calendar appointments to get out of sync leading to common Calendar errors such as "Cannot update the appointment because the corresponding item in the folder you synchronized does not match the item" or "Conflicting edits have been made to the same item.  To resolve this conflict, select the item in the list below you wish to keep and then choose..."  This occurs for just normal senders and recipients of calendar appointments with BES in place.  When the originator of the meeting (or a delegate of the meeting) gets this conflict of meetings and chooses one versus the other appointment, effectively the user is choosing to keep 1 appointment and delete another appointment, which then sends a meeting deletion to all users connected to that appointment (which as noted earlier in this post, in split calendar appointment scenarios caused by cross-platform errors, one of the meeting appointments could go to Mac users with a different meeting appointment going to Windows users, thus creating differences in results dependent on the client the user is running).

In a manager/delegate situation, the problem is even worse as both the manager and delegate have full read/write/edit capabilities to appointments so that when a delegate accepts a meeting of their boss on a Blackberry device, or changes a meeting request of their manager from a Blackberry device, the delay time back to Exchange changes the attributes of the meeting request effectively modifying a portion of the meeting, not the entire meeting, which creates the sync, attribute, conflict errors noted above.

Solution:  For Blackberry devices in a manager/delegate calendar sharing environment, it is best to NOT use the Blackberry device to manage meeting requests of shared delegates (ie: don't accept, reject, change, or create meetings as a delegate of another individual from a Blackberry device).  Effectively do ALL delegate calendar management from a desktop computer running the EXACT same version of Outlook as the manager.  If the manager is running Outlook 2007, the delegate should do all calendar accepts/rejects/edits from a computer running Outlook 2007.  If the manager is running a Mac, the delegate should do all calendar accepts/rejects/edits for that manager on a Mac.  Any time a different version/platform of operating system or mail client is used, calendar corruption can occur.

I note "can occur" as the problem happens most frequently when the Blackberry server and Exchange server(s) are busy and queue times lengthen, and the problems don't always occur late in the afternoon or evening when IT is trying to debug the problem, no one is on the network, and the problem doesn't show up.  The problems occur most frequently when the Blackberry server is at its highest capacity.  Check the Blackberry message queue to see when message transfer and processing is delayed due to message queue build-up.

Exchange 2010 Bug

For organizations that have migrated to Exchange 2010 and having odd calendar delegate problems, there was a bug that was introduced in Exchange 2010 with Roll-up 1 (in December 2009) and persisted until it was fixed in Roll-up 4 (in June 2010).  The problem has to do with how meeting delegates accepted or rejected meeting invites.  If a delegate is the delegate managing multiple calendars and a meeting is sent to multiple "Managers", only ONE copy of the meeting invite will be received by the delegate (historically, alphabetically so that the "first" invite is received), and subsequent invites are "lost".  So only 1 of the "Managers" accept the invitation and all others end up in limbo, typically the meeting just doesn't show up in the person's calendar even though the assistant knows they accepted the invite (unfortunately the assistant accepted the only copy of the invite received, not ALL of the invites for all of the people the assistant is delegate for because this Exchange bug didn't send multiple copies of the meeting invite as Exchange should have).  Similarly, if the Manager and the Delegate get invited to the same meeting, only 1 of the invites will be received by the delegate, either for the Manager or for the delegate, but not both.  So only 1 of the two will end up accepting the invitation and the invite won't end up on one of the two individual's calendar.

This bug was fixed in Roll-up 4 in June 2010 and addresses this problem, however for several months, and for many organizations rolling out Exchange 2010, this error still haunts them as an inconsistent quirk.  Quite frequently, this error still occurs when organizations have some systems updated with the latest Exchange roll-out, but not all systems have been updated to Roll-up 4 or more current, and as such, the quirky nature of this problem is inconsistent dependent on the roll-up level of the server the user is accessing.  For more information, see

Performance Issue with Exchange Calendaring

A specific item to note about Exchange calendaring access is one that involves Exchange calendar access performance.  Users complain that accessing the calendar of another indivividual takes a lot time (upwards of 20-30 seconds).  A default setting in Outlook 2007 and Outlook 2010 when a user is running Cachemode for Outlook is a setting that caches "Shared Folders".  It is selected by default and when a user opens another person's calendar, it downloads the other person's entire calendar so that it does a Cachemode on other user's calendars.  This is great if you work offline and want to potentially look at someone else's calendar, however when a user is online, each and every time another calendar is open, Outlook goes out to the other user's calendar, checks for changes, and does a complete calendar synchronization before the user's calendar is visible.  This is frequently reported as "slow performance for calendar access" as it can be 5, 10, 20 seconds before a user's calendar appointments are visible.

The solution to this problem is to turn off the caching of Shared Folders by going into the Outlook profile (File / Info / Account Settings in Outlook 2010; or Tools / Options / Account Settings in Outlook 2003 or 2007), click on the Advanced Tab, and uncheck the Download Shared Folders checkbox as shown in the graphic below.

Other Issues with Calendaring in Outlook and Exchange

There are several other issues inter-related between calendaring problems and Exchange performance problems.  Take a look at the posting I refer to at the start of this post about Exchange/Outlook performance, specifically server hardware / LAN-WAN performance issues and the Frequently Asked Questions.

Hopefully this is a place to start when trying to understand why calendaring in Exchange is inconsistent, and know there are fixes and solutions to them ALL as we have helped dozens of organizations better understand why the problems exist so that the organizations can fix the problems and ultimately end up with a 100% reliable calendar environment in Exchange.

iOS Fix Solves Duplicate / Missing Calendar Issues in iPads/iPhones

{Added 5/11/2011}  Apple fixed a long standing "bug" in their iOS with v4.3 in April 2011.  All previous versions of the iOS on iPads and iPhones created a situation where recurring calendar appointments would be completely deleted if a user simply deleted just a single occurrence.  This bug fix specifically mentions interactions of problems between iPads/iPhones and Blackberry/BES devices.  See

Frequently Asked Questions:

Q:  How come all of a sudden these calendar problems have become a big thing?

A:  Calendaring and Exchange performance issues ballooned up June/July of 2010 due in part to a bug in the iPhone 4.0 operating system that effectly locked up access for mobile users cause delays of mobile devices to Exchange and overall performance issues to Exchange in general (see my blog post or Apple technote for more details).  I call this the straw that broke the camel's back, although other factors such as more and more Apple Macs popping up on networks (particularly with executives, while their admins are running Windows), more use of Blackberries, etc.  Basically little by little the problem has grown until the iPhone problem has caused hundreds of companies to contact me in the past 5 weeks alone on these issues

Q:  All of our executives and their assistants have Windows-based systems (no Macs), and all of the execs have gotten rid of their Blackberries and now use iPhones or Windows Mobile devices, yet we still have calendar problems, what's up?

A:  Key things to check is that your execs and assistants are running the exact same version of Outlook (if Outlook 2007, then make sure you are 100% Outlook 2007 between execs and assistants), if an assistant is running Outlook 2003, or Outlook 2010, basically a different version of Outlook, that matters.  Additionally, we have found in many cases where an assistant is using a Blackberry to accept meeting invites of executives, that as noted is a known problem.  Lastly, check your Blackberry server and see if your execs and admins truly have had their Blackberry accounts removed.  I have seen several cases where the execs and assistants got rid of their Blackberries months earlier, yet the user's Blackberry account was never deleted, so effectively the Blackberry server is still grabbing calendar appointments and sending them off to RIM to go to never neverland.  Make sure you have a clean deprovisioning process for devices once a user stops using the device.  (same goes true with ActiveSync, I've seen orgs where a user never deleted their old Windows Mobile or iPhone device, and to this day the Exchange server is sending calendar appointments out to several ActiveSync devices for the user despite the user only having 1 device)

Q:  Okay, so we don't have Macs, we've cleaned up our Blackberry administration, we've cleaned up ActiveSync, yet users are still complaining that appointments are still missing or creating duplicates, what's up now?

A:  Even after you clean everything up, it's a good 3-6 weeks before complaints die down.  Remember, user's appointments likely were booked 2-3 weeks ago for a meeting that was just supposed to happen, and 2-3 weeks ago things were screwed up and the appointment lost way back then, so roll forward to today, the complaint is really about a problem that happened a few weeks ago.  The problem lingers for a few weeks until all historical stuff works their way out of the system, we usually find this to be 3-6 weeks before the compliants disappear.

Q:  Okay, we've now waited 2 months, we're still having odd problems, do we have ghosts in our system?

A:  Yes, possibly, in several instances of persistent problems we found that a previous delegate/assistant setup a bunch of Inbox rules in Outlook as well as on their Blackberry device to auto-accept appointments, or auto-move appointments that were pushed up as server-based rules.  Months later, those rules were still up on the server (despite that assistant no longer working for the company) and the delegate rule was never removed and the rules never deleted, so the rules to manage appointments continue.  With Exchange 2007 and Exchange 2010, you can run PowerShell to view all delegates as well as view server-based rules.  With Exchange 2003, it's a little harder where you have to turn on server logging and then come back a couple days later to view the logs.  But effectively, don't forget about "rules" created by delegates long gone from the organization.

Q:  Shouldn't Microsoft fix these problems with Outlook / Entourage / Exchange / Blackberry / iPhone / etc?

A:  Well it's hard for Microsoft to fix things with Blacbkerry and iPhones, but overall the industry is heading toward processes to FIX/Minimize/Eliminate these calendaring problems.  Microsoft came out with Outlook 2011 for the Mac that was a huge step forward in improving the Mac Office 2011 / Windows Office 2010 compatibility, however it's a LOT (lot!) better, but still not perfect.  Beyond looking like Outlook for Windows, many of the attributes between Outlook 2011 for the Mac and Outlook for Windows have been standardized, thus getting Outlook "closer" between platforms.  And as mentioned earlier in this post, Research in Motion will be releasing a long awaited update to the BES server that'll use a more secure, better method of connecting a BES server to Exchange that'll minimize the impact Blackberry has with Exchange.  And as long as Apple doesn't work in more bugs to ActiveSync for their iPhone iOS, the ActiveSync functions with iPhones / iPads continues to improve with better compatibility.  However, until everything is really truly working together, keeping executive/assistant pairs matched up with the same Windows or Mac platform, and same Office / client platform is currently the only way to ensure clean calendaring with Exchange.

Q:  Sounds like we should move our mail to the cloud and completely do away with these Exchange problems.

A:  Unfortuantely the cloud is no better than internal Exchange.  If you use Exchange in the cloud and use Macs, Windows, buggy iPhones, the problems persist in the cloud (as we have painfully experienced over the past 6 weeks with Exchange cloud vendors slammed with outages caused by the iPhone bug), so the cloud doesn't fix the problem.  You can always go to gmail in the cloud, although gmail doesn't have a good enterprise calendar solution for doing calendar delegates or enterprise meeting scheduling, so I guess your calendar problem goes away with gmail because you really can't do enterprise calendar delegation and sharing on gmail, but I don't think this is the solution.  No need to run from the problem when there are known fixes to make Exchange calendaring reliable and dependable.

Q:  Has anything changed since you initially wrote this article in the summer of 2010?

A:  Yes, I've since updated this article 6-7 times (latest updated is March 2011), so I'm trying to keep this article up to date on the most curernt known information.  In fact, Apple just released a new update to the iPhone/iPad iOS last week (March 2011) that addresses "most" of what I noted above as bugs we were aware of back in January/February 2011, but they did not fix a couple others.  Blackberry has released a half dozen updates since I first posted this blog post, and each time their fixes solve some problems, but then create new ones.  The latest version of Exchange 2010 (service pack and roll-ups) has proven stable and addressed several problems with calendaring and performance.  Knock on wood that no other issues crop up with the latest release, so far, so good.  Bottomline though, the calendar issues organizations run in to is NOT a mystery.  While the vendors don't openly admit the problems, if you follow the trail of tech note links to each of their sites (Apple, RIM, Microsoft), they know of the problems and are fixing the issues, they're just not outright making a big deal of it as I'm sure if they did, their phones will be off the hook.

Q:  Can we get to the point where calendaring is reliable?

A:  Absolutely, we have made enterprise calendaring in Exchange work reliably and dependably for years for small, medium, and really really large enterprises.  Once the organization understands the root cause of the problems (that I've noted above) and they put in place a process to standardize configurations for delegates, and clean up various versions of the client software, calendar problems for these organizations have gone away.  Calendaring problems are not a mystery, just no one has ever clearly explained why the problems exist for organizations to put a plan in place to fix the problems.  Hopefully this posting clarifies the background and will help your organization get on a road to reliable and dependable calendaring!

The author of this post is Rand Morimoto, President of Convergent Computing ( and author of the bestselling books "Exchange 2010 Unleashed", "Windows 2008 R2 Unleashed", "System Center Enterprise Suite Unleashed", and dozens of other books on Windows, Exchange, security, systems management, and the like.  Rand and the consultants in his company work with Exchange 2-3 years before the product's release and thus are very familiar with the underpinnings of Exchange, the quirks, and the workarounds to make Exchange work in large scale environments.  Rand is also VERY familiar with Apple Mac systems, despite writing best selling books on Windows 7 and every version of Windows for the past dozen+ years, Rand uses a MacBook Air as his primary client system, Office 2011 Mac (and Mac Mail App) for his mail client(s), and uses an Apple MacPro Server to test (and demonstrate) the latest versions of Microsoft Exchange giving Rand firsthand knowledge on how to make a mixed/multi-platform environment work as expected.

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