Why does add in still appear and work in both new Outlook desktop and new Outlook web but not Outlook Classic?

Question

I use Outlook Classic desktop in Office 365 w/ desktop apps. I have used Clio's Outlook add in for 2 yrs. Recently the add in disappeared from my Outlook Classic desktop. The add in still appears and works if I use either new Outlook desktop or new Outlook web.

In Classic Outlook desktop, when I select File/Options/Add ins, Clio is no longer listed and there are no Disabled Applications Add Ins listed.

In Classic Outlook desktop, when I select Home/All Apps it says I have no apps installed. It used to list Clio Outlook add in however in new Outlook desktop, when I select Home/All Apps it says Clio Outlook add in is installed.

In Classic Outlook desktop, when I select Home/All Apps/Add Apps and try to install any of the add ins from the list I get "Something went wrong, Please try again later"

When I try to install add ins to Outlook Classic from the Microsoft Marketplace it takes me to Microsoft 365 admin center where it says "We are unable to initiate the deployment"

Why will Outlook Classic desktop not allow me to install any add ins?

Answer 1

Hi Phil,

Based on your sharing, this behavior likely points to classic Outlook failing to read/write Office web add-ins for your mailbox/tenant. The fact that Clio still works in new Outlook and Outlook on the web means the add-in truly exists, but classic Outlook's add-in discovery/deployment path is blocked, broken or not receiving the add-in metadata.

After my investigation, I suspect that your classic Outlook may be hitting a current Microsoft Office Add-ins service issue. Refer to Office Add-ins known issues - Office Add-ins | Microsoft Learn, there has been a recent Office Add-ins issue where centrally deployed or organization-managed add-ins can disappear from the ribbon, fail to load, or not appear even through deployment remains assigned. That maps closely to your symptoms that:

• Clio disappeared only from classic Outlook
• No installed app in All Apps
• Adding attempts give "Something went wrong" error message
• Marketplace deployment fails before initiating.

There are some workarounds suggested by Microsoft that you may try to see if it helps:

• Restart the Office application.
• Refresh admin-managed add-ins from the add-ins pane.
• Wait and retry after some time while mitigations continue to roll out.
• Verify the user has access to required Microsoft 365 and Exchange Online services.
• If your organization restricts Exchange Web Services (EWS), verify required access settings are enabled.

If the issue still persists, for you to receive the best possible assistance, I highly recommend asking the Global Admin in your organization create a service request with Microsoft Support for advanced diagnosis. A technical support engineer can initiate a remote session to review the issue in detail, confirm the backend configurations, and run any required synchronization tools to help resolve the problem. If additional expertise is needed, they can involve the appropriate specialized team for deeper investigation. 

In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support   

• To create a support ticket to Microsoft, please sign into Microsoft 365 Admin Center > at the bottom-right, select the Help & Support button (green icon) > Contact Support. 
• For detailed instructions on how to create a support ticket, please refer to Get support - Microsoft 365 admin.  

I genuinely wish I could directly delve into the backend systems to diagnose and fix this for you. However, as a forum moderator, my role here is limited to providing general guidance and solutions that can be applied by users. Please know that even though I can't directly intervene, directing you to the correct, specialized support is the most effective help I can provide from my position. 

Thank you for your understanding and I truly hope the issue will be resolved swiftly.

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Answer 2

Thank you, I will create a service request with Microsoft Support