Shared mailbox categories no longer working

Hi @Speckmann, Frea, 

Welcome to the Microsoft Q&A forum.  

Thank you for the clear details and for testing the Outlook profile reset workaround, that effort is very helpful for narrowing down the cause. Based on your description, since Monday 26 January multiple users cannot add categories to emails in shared mailboxes because the Categories option is greyed out in the new Outlook.  

In many cases, this occurs when the new Outlook does not successfully refresh the category metadata for a shared mailbox, even though permissions and configuration remain unchanged. As a result, the app may temporarily treat the shared mailbox category list as unavailable, which then disables the Categories control. Consequently, rebuilding the profile helps because it forces a clean synchronization, but it is understandably not a practical long term approach for multiple users. 

To address this in a more sustainable way, please follow the workarounds below in order, since each step builds on the previous one. 

1/ Verify whether the issue is app specific or mailbox specific 

• Sign in to Outlook on the web. 
• Open the shared mailbox and select any email. 
• Try to assign a category to that email. 
• Record the outcome. 

If categories work in Outlook on the web, this indicates the mailbox is healthy and the behavior is primarily related to synchronization in the new Outlook client. 

2/ Reconnect the shared mailbox within the new Outlook 

• In the new Outlook, open Settings. 
• Select Accounts, then open Shared mailboxes. 
• Remove the affected shared mailbox from the list. 
• Close the new Outlook completely and then reopen it. 
• Add the shared mailbox again, then allow a few minutes for sync to complete before testing Categories. 

This refreshes the shared mailbox connection and often restores access to the category picker without rebuilding the entire profile. 

3/ Force a category list refresh for the shared mailbox 

• In Outlook on the web, open the shared mailbox context. 
• Go to Settings, then View all Outlook settings. 
• Select General, then Categories. 
• Create a new test category, for example Shared Test, and save it. 
• Return to the new Outlook app, close and reopen it, then check whether Categories is enabled and whether the new category appears. 

This change prompts the service to republish the category list, which can trigger the new Outlook to pick up the updated metadata. 

4/ Clear local Outlook data for the new Outlook and allow a fresh sync 

• In the new Outlook, go to Settings, then General. 
• Open Privacy and data and select the option to clear locally stored Outlook data for the new Outlook. 
• Restart the new Outlook, open the shared mailbox, and allow time for the mailbox data to synchronize before testing again. 

This targets local cache inconsistencies and typically provides the same benefit as a profile rebuild, while being more repeatable at scale. 

If the issue persists after completing these steps, please share the following details so I can guide the next action quickly: New Outlook version, whether categories work in Outlook on the web for the same shared mailbox, and whether the behavior affects all shared mailboxes or only specific ones. 

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.      

Thank you for your patience and your understanding. I look forward to continuing the conversation. 

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I'd like to add additional information regarding this issue. For our organization this already started back in november 2025 not just January. So far only 2 users are affected in the org.

The issue is localized only to New Outlook. Any user switching back to classic outlook regains the capabilities to categorize emails.

If the user opens the shared email box in OWA, outlok for web, the categorization functions perfectly, same with opening the shared box in any other email client with support, this only happens as I said in new Outlook and can't be replicated spcifically.

For us this affects one long term user more than 6 years and one user less than a year.

Removing access to the shared emailbox and having user restart their client and then re-allocating access and restarting the client leads to the user being able to categorize again for a day max quite consistently.

We have also done repair client, uninstall client and they are all temporary fixes, after 24h the problem returns again.

One solution I am looking into now is to schedule with powershell the removal and re-allocaion of shared emailboxes for users every 4 hours and scheduling a restart of their new outlook clients at the same hour of the day as this hsa the same effect as me doing it manually.

It is a shame it has been so long to fix this issue as it has a great effect on the business and even when I created a case in the admin portal microsoft responded with the issue not existing as they could not replicate it themselves.