User Mailbox Issue: Specific Emails Not Appearing on Desktop App

Question

I am IT admin for my organization. I am troubleshooting an issue multiple end users have experienced with an Outlook mailbox on Windows 11 PCs. The mailbox is a User Mailbox that has several delegates and is treated as a Shared Mailbox. For our PCs, we use Outlook Classic exclusively and do not use OWA or Outlook New.

The issue: On the desktop client, all end users (~10 people) with access to a specific mailbox cannot view two emails inside said mailbox. However, the email appears fine when viewing the mailbox on Outlook's mobile app.

It's possible to search for the missing emails on the desktop client. The emails appear fine on the search, but when attempting to open them, we receive this error:

I have confirmed this error appears when attempting to open the same email across three different accounts.

Also, the M365 version for a majority of affected end users is 16.0.19628.20166. Versions vary for the remaining affected end users.

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Before I realized the issue was affecting all end users with this User mailbox access, I worked with one end user. These are the troubleshooting steps we went through:

-Disabled cached exchange mode/rebooted Outlook

-Deleted RoamCache contents

-Renamed OST file to .old, then re-enabled cached exchanged mode

-Unchecked download shared folders

-Delete Outlook profile in Control Panel

-Log back into Outlook account

-Re-enable download shared folders

-Run quick repair on Outlook

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At this point, I assume the issue is with the mailbox itself, but I'm not sure how to proceed. One possible clue was the mailbox usage, but I'm under the assumption the utilization is low enough not to have issues: ‎30.44 GB‎/‎49.5 GB‎ (‎61.50‎% used).

Any suggestions or guidance regarding this problem would be greatly appreciated.

Answer 1

Hi @Sarah Sagan

Thank you for posting your question in the Q&A Forum and outlining all the troubleshooting steps you’ve already tried.

Since the issue affects all users in Classic Outlook, while the same messages open normally in Outlook Mobile, this indicates that the issue is not related to a local client configuration. Instead, it appears to be specific to how those individual items are being accessed through Classic Outlook.

Classic Outlook and Outlook Mobile connect to Exchange using different methods. In some cases, when a message cannot be opened in Classic Outlook but displays correctly in Mobile, moving the item can prompt Exchange to refresh how the message is processed. As a quick test, please try the following:

Move the affected emails using Outlook Mobile (or Outlook on the Web):

• Open the shared mailbox in Outlook Mobile.
• Locate the two affected messages.
• Move them to a new or temporary folder within the same mailbox.
• After doing so, check again in Classic Outlook to see if they open normally.

In many similar scenarios, simply moving the items causes Exchange to regenerate the associated metadata, and the messages become accessible immediately.

If the behavior persists after attempting this step, feel free to update the thread and we can look into additional options from there.

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