Categories in Shared Mailbox in Outlook

Question

Hey,

I would like to ask for clarification and guidance due to the inconsistent behavior with email categories in a shared mailbox.

The environment: Microsoft Outlook with shared mailbox used by multiple users. Additionally those users have different versions of the Outlook (classic and new).

Categories are used to mark incoming requests for ownership assignment.

Observed issue: Categories applied to message in the shared mailbox sometimes appear to revert, reappear or differ between users.
Sometimes category that was manually changed/removed appears again after replying or receiving a new message in the conversation.

The issue is not consistently reproducible, which makes me confused - basically I dont understand what is going on, and why.

From what I know, categories are not tied simply to one message, since we are seeing the categories to be automatically assigned to the entire thread. But after manual changes seeing auto reverts is creating confusion.

Are there any rules related to categories? Know features that would enable me creation of workarounds? Or is it simply a sync issue, and it will work like that no matter what.

Any guidance, documentation or best practices for using categories in shared mailboxes would be greatly appreciated.

Thank You.

Answer 1

Hello @Jakub Jakubek, 

Thank you for your patience while I reviewed this issue. 

Based on your description, I’ve tested the scenario in a controlled environment, and everything seems consistent there, which suggests the problem is not universal but likely tied to a specific environment. 

Here some basic troubleshooting steps you can try: 

Test Sync 

• In New Outlook, go to View > Sync and trigger manual sync. 
• Wait 5 - 10 minutes and recheck category state. 

Turn off Enable offline email, calendar, and people:  

• Open New Outlook for Windows.  
• Click on the Settings (gear icon) in the top-right corner.  
• Scroll down and select General > Offiline.  
• Find the option Enable offline email, calendar, and people.  
• Toggle it OFF.  
• Restart Outlook to apply the changes.  

  

 Manually repair your Outlook App  

• Press Windows + I to open the Settings app.  
• Click on Apps > Installed apps (or Apps & features, depending on your Windows version).  
• Scroll down or search for Outlook for Windows > Click on the three dots > Advanced options   
• Scroll down to the Reset section > Choose Repair  

Alternatively, you can remove the shared mailbox from your account settings and then re-add it: Access a shared mailbox in Outlook - Microsoft Support 

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If the issue persists, it appears that this issue requires a deeper investigation on the backend. I recommend reaching out to the Microsoft Technical Support Team for further assistance. Their specialists can perform deeper diagnostics and, if needed, escalate the case to the appropriate internal team for further analysis. This ensures the issue is formally tracked and may contribute to a future fix.  

For business support:  

• Find your Microsoft 365 admin: If you don't know who the global admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support   
• Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn   
• If your organization's Office 365 Business/Education subscription is from a partner or reseller, and the global administrator is unable to open a service request on your end, contact the reseller's support provider to help open a service request on behalf of you instead.   

If you discover any solutions or have additional insights, please consider replying to this thread to help others in the community.  

I sincerely apologize for redirecting you to the Microsoft Technical Support Team. While I strive to assist as much as possible here in the forum, my resources are limited when it comes to backend-level diagnostics and advanced troubleshooting. Some issues require deeper technical analysis and access to internal tools that only the official support team can provide. 

If you need further assistance, feel free to reply. I'm here and happy to help!

Answer 2

Hello @Jakub Jakubek, 

Good day! Thank you for posting your valuable question on the Microsoft Q&A forum. 

Based on your description, I understand that your environment is Microsoft Outlook with a shared mailbox accessed by multiple users, and those users are on different Outlook versions (Classic and New). Categories are being used to mark incoming requests for ownership assignment, but you’re seeing inconsistent behavior where categories revert or differ between users.

Please let me know if I misunderstood any part of your situation or you have any additional information to share. 

To help us perform the accurate testing environment, could you confirm the following: 

• Is the shared mailbox added as a folder under your account or as a separate account in Outlook? 
• Do all users have Full Access permissions to the shared mailbox, or are some using Delegate permissions? 
• Can every user apply and modify categories in the shared mailbox, or only certain users have that ability? 
• Are categories propagating across the entire conversation or only on individual messages? 
• Are the users using the same operating system?
• Could you also check if there are any mailbox rules applied that add or modify categories automatically? You can perform this action by navigating to Home tab > Rules > Manage Rules for New Outlook or Manage Rules and Alert for Classic Outlook 

This additional context will help us understand your environment and the steps already taken so we can tailor the guidance to resolve the issue effectively. 

In the meantime, here are some basic checks you can try: 

• Make sure categories are predefined in the shared mailbox by a user with Full Access. This ensures consistency across all users. 
• Turn off Conversation View temporarily and see if the behavior changes. 
• If using New Outlook, consider adding the shared mailbox as an account rather than just a folder for better category sync. 
• Confirm that all users have the same category list defined in their Outlook client. 

I apologize if I could not jump straight to a solution. I want to avoid suggesting anything that might be inaccurate or unhelpful. Once we have the details above, we’ll be able to assist you more effectively and guide you toward the right resolution. 

Looking forward to your response so we can get this sorted out together. 

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