Cowork Not Delivered Message

We are seeing the same but the interesting thing is that if we look in the iPadOS Copilot app, the requests are being accepted and you can see the tasks being carried out. Might be worth checking but we're working with Microsoft on this.

We had the same issue for weeks, very frustrating, and a fix was found. Below are the resolution details:

Resolution – Cowork “Not delivered / no response” issue

We’ve resolved this in our tenant and wanted to share the outcome.

Root cause

The issue was network security (Netskope) blocking Cowork’s runtime endpoints.

Symptoms observed:

• “Not delivered. Retry?”
• No response when submitting prompts
• Often fails on the second message
• Copilot Chat and other agents worked normally

This occurs because Cowork uses a different backend runtime path from standard Copilot Chat.

Fix

We resolved this by allowlisting the required Cowork endpoints.

Microsoft documentation

• Cowork network endpoints:
  https://support.microsoft.com/en-us/topic/cowork-network-endpoints-48dd7f76-1322-4c63-945b-d781632f501a

From Microsoft guidance, the required endpoints include:

m365.cloud.microsoft.com 

login.microsoftonline.com 

graph.microsoft.com 

*.gateway.prod.island.powerapps.com:443

The critical endpoint is:

*.gateway.prod.island.powerapps.com

Microsoft notes:

• This endpoint is used for Cowork routing and runtime
• Routing is dynamic by user and region
• Do not restrict to specific subdomains https://support.microsoft.com/en-us/topic/cowork-network-endpoints-48dd7f76-1322-4c63-945b-d781632f501a

Important behaviour observed

Once the endpoint was allowlisted:

• All previously failed and pending messages immediately appeared and processed in Cowork

This indicates:

• Requests were reaching the service
• Execution was blocked at the runtime layer
• Cowork queued and completed the tasks once connectivity was restored

Supporting references

• Community thread showing “Not delivered. Retry?” and second‑message failure pattern:
  Cowork Not Delivered Message (TechCommunity)
• Microsoft Learn guidance acknowledging cases where Cowork can be unresponsive or stuck:
  https://learn.microsoft.com/en-us/microsoft-365/copilot/cowork/best-practices

Recommendation

If Cowork is not working but Copilot Chat is:

• Review proxy / CASB / firewall configuration (for example, Netskope)
• Ensure this endpoint is allowed or bypassed:

*.gateway.prod.island.powerapps.com

• Validate that no SSL inspection or Conditional Access policy is interfering with this path

Notes

Cowork is currently a Frontier (preview) feature, and Microsoft notes:

• Behaviour may vary across users
• Rollout is region-based
• Backend routing is dynamic
  https://support.microsoft.com/en-us/topic/get-started-with-cowork-frontier-60be4cea-b913-471b-a0d8-f9ab73c6b0be

Summary

This is not a client, cache, or reinstall issue.

It is a network path dependency specific to Cowork, and can fail independently of the rest of Copilot.

Yes happening for us as well across all enabled Anthropic/Frontier users and very frustrating. When opening the agent, the recent tasks section just has the purple animation, but never loads. Interestingly, when I ask Cowork to draft an email, it goes away and thinks for a while before coming back with the "Not delivered, retry?" message, but I do get the email created in my Drafts folder in Outlook. It seems to me like the Agent can't connect to the backend processing to get messages, results etc. I've asked our security team to check if there are URLs getting blocked or something.

I'm seeing the same thing, particularly when sending a second message.