Severe Outlook for Mac issue

Sometimes things going wrong. So this time with Outlook for Mac. Starting with version 16.22 from Insider Slow we started seen some strange behavior as suddenly additional entries in the calendar view occurred. But with version 16.23 things got even worse.

When your mailbox is in Exchange Online and you are using Outlook for Mac with this version, you should continue reading. I f not you can relax and stop reading.


There is now a new version available, which has a fix for this:

Make sure you install version 16.23.326.1!


Microsoft made some improvements in the way how calendar sharing works in Exchange Online (On-Premises is not getting this!). You can read more about here:

The improvements in a nutshell means that a shared calendar is copied to your mailbox into a folder underneath your own calendar. This way you reduce the number of connections, which are usually needed to access shared calendars, and make this available to other clients. That’s how Outlook for Mobile gained access to shared calendars.

Having this said, with this new version of Outlook for Mac, a user is lifted to the new calendar experience. Thus means also the view in your calendar changes.

The culprit

With this version Outlook for Mac changes calendar view. It now shows also “old” links from OWA or Outlook for Windows, when you added a shared calendar to your list. Sadly also those new folders with the synchronized calendar will be shown in the very same way. Thus means users suddenly see a bunch of entries and some will start a cleanup. No problem with these old links, but when you delete one of the folders and you have also Editor permission, a deletion of the items in the shared calendar might be triggered and data loss occurs.

Today a KB article was published:

If a shared calendar is removed, events may get deleted on the owner’s calendar

And now also the list of features and add-ins list:

Outlook for Mac features and add-ins issues

Therefore I highly recommend to hold off deploying this version and if already happened, advise your users to not delete any calendar!


As previously mentioned thing can go wrong. in this case it’s NOT a service (Exchange Online) or the new calendar sharing improvements issue. It’s a pure client issue. Microsoft is working hard to get the client fixed. For now you can only spread the workaround (using OWA) or the info not to delete any calendar until this has been fixed.

5 thoughts on “Severe Outlook for Mac issue

  1. Pingback: Severe Outlook for Mac issue | The clueless guy – JC's Blog-O-Gibberish

  2. Great article and thank you for spelling this out. Wondering if you have heard of this odd issue, because a few Google searches and I’m coming up with nothing yet. Not even my own IT team has an idea how to fix/repair this. I have a shared calendar that is its own account on our server. Since 16.2, when i go to permissions…they are gone. So i can’t add new people to the calendar. Wondering if you have possibly heard of this?


    • Hi Shawn, this came with the updated version? Are you sure you have the necessary permissions for this shared mailbox? I couldn’t repro the behavior, but maybe I have a different setup, which doesn’t have this issue. You can contact me offline if you want.


      • Ended up finding a work around here. Went into Accounts -> Advanced -> Delegates Tab -> Added the shared calendar under “Open these additional mailboxes”. Per my IT team it looks MSFT messed something up and they are looking into it.


      • Hey Shawn,
        this sounds to me that your mailbox is in a different location than the shared one. Like you’re in EXO and the shared is on-premises!?
        If so, this is not their fault….it’s by design. There are also similar issues with Outlook on Windows…this reminds me of another post about exactly these issues.


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