Table of Contents
Introduction
Microsoft says it's still investigating a known issue that causes the Copilot and Copilot Chat buttons in classic Outlook to disappear for some Windows users.
As it acknowledged when it announced a fix via a service change in June, this affects only customers with the Copilot Chat (Basic) license or a paid M365 Copilot (Premium) account who may no longer see the Copilot buttons in the side navigation and above the ribbon.
This blog is based on reporting by Sergiu Gatlan (September 16, 2026). Microsoft has confirmed the issue and is actively investigating.
Who Is Affected?
The issue specifically affects classic Outlook for Windows users who have one of the following licenses:
- Copilot Chat (Basic) — Free or basic Copilot access
- M365 Copilot (Premium) — Paid Microsoft 365 Copilot subscription
Microsoft confirmed the issue occurs after upgrading classic Outlook for Windows to build 20026.20182 and higher.
If you're on an older build of classic Outlook, you are not affected by this specific bug — but you may still want to update for security reasons.
Symptoms You May Experience
According to Microsoft, affected users may experience one or more of the following issues:
| Symptom | Description |
|---|---|
| Missing ribbon button | The Copilot button is missing from the top-right area above the ribbon |
| Missing app bar icon | The Copilot icon is missing from the left app bar or More Apps area |
| Dead "Open" action | In Add Apps, Copilot may appear as available, but selecting Open does nothing |
| Grayed-out command | Adding Copilot through ribbon customization may show the command as unavailable |
| Other entry points work | Copilot remains available via Outlook on the web or the Microsoft 365 Copilot app |
The good news: Copilot is still accessible through other entry points, including Outlook on the web and the Microsoft 365 Copilot standalone app or web experience.
The Root Cause: A Missing MAPI Property
Microsoft has identified the likely cause of the issue. In a recent update, the company said:
"The Outlook Team is actively investigating this issue. Current analysis indicates that, in affected environments, Outlook is unable to locate the MAPI property PR_PROFILE_USER_SMTP_EMAIL_ADDRESS_W within the null profile section."
— Microsoft"As a result, the Outlook Copilot component cannot persist in Copilot-related settings, which may prevent the Copilot entry point from appearing in the Outlook navigation pane."
— MicrosoftIn simpler terms: Outlook is failing to read a specific profile setting related to your email address, which breaks the Copilot component's ability to save its configuration — so the button simply doesn't appear.
Temporary Workaround
While Microsoft works on a permanent fix, the company has shared a temporary workaround that requires enabling the "Show Apps in Outlook" option in classic Outlook settings.
How to Enable "Show Apps in Outlook"
- Open classic Outlook for Windows
- Select the File tab
- Click Options
- Go to Advanced
- Under "Outlook panes", check the box for "Show Apps in Outlook"
- Click OK and restart Outlook if prompted
After enabling this option, the Copilot button should reappear in the navigation pane for most affected users.
Alternative Workarounds
If the "Show Apps in Outlook" workaround doesn't resolve the issue, Microsoft suggests two additional options:
- Create a new Outlook profile — A fresh profile can sometimes resolve the missing MAPI property issue
- Use the new Outlook or Outlook Web Access (OWA) — Neither is affected by this bug, so Copilot works normally there
The new Outlook for Windows and OWA are both unaffected by this specific issue. If you need Copilot urgently, switching to one of these clients is the fastest path.
Related: Kaspersky Antivirus Crash Bug
In the same update, Microsoft also confirmed a separate bug that causes unexpected Outlook crashes on systems running Kaspersky Antivirus software.
The crashes trigger "Event 1000" events in the Application log linked to the Kaspersky Mail Checker (mcou.dll).
Although the Outlook Team is still investigating, it advised Kaspersky customers experiencing crashes to contact Kaspersky support directly.
Earlier this year, Microsoft also resolved known issues that:
- Rendered the classic Outlook client unusable when enabling the Microsoft Teams Meeting Add-in
- Prevented some classic Outlook users from sending emails via Outlook.com
What Businesses Should Do
If your organization relies on Copilot in classic Outlook, here's a practical checklist:
- Check your Outlook build — If you're on build 20026.20182 or higher, you may be affected
- Apply the workaround — Enable "Show Apps in Outlook" for affected users
- Communicate to staff — Let users know Copilot is still available via OWA and the new Outlook
- Consider the new Outlook — If your organization is ready, the new Outlook is not affected
- Monitor for a permanent fix — Microsoft is actively investigating and will release a fix
- Check Kaspersky compatibility — If you run Kaspersky Antivirus, watch for Outlook crash events
- Document the issue — Keep a record of affected users and workarounds applied
If your business needs help managing Microsoft 365 Copilot deployments or Outlook issues, consider working with a managed IT partner.
Final Thoughts
The missing Copilot buttons in classic Outlook are a frustrating but temporary issue. Microsoft has identified the root cause, provided a workaround, and is actively working on a permanent fix.
Key takeaways:
- Affected users — Copilot Chat (Basic) or M365 Copilot (Premium) on classic Outlook build 20026.20182+
- Symptoms — Missing Copilot button above ribbon, missing icon in app bar, grayed-out commands
- Root cause — Outlook can't locate the MAPI property PR_PROFILE_USER_SMTP_EMAIL_ADDRESS_W
- Workaround — Enable "Show Apps in Outlook" in File → Options → Advanced
- Alternatives — Create a new profile, or use new Outlook / OWA
- Separate bug — Kaspersky Antivirus causing Outlook crashes (mcou.dll)
- Permanent fix — Microsoft is actively investigating
If your organization needs help with Microsoft 365, Copilot deployment, or Outlook troubleshooting, contact SystemLogicIT for expert guidance across the United States and United Kingdom.