Copilot buttons keep vanishing from classic Outlook, and Microsoft still can't say why
A build upgrade is hiding paid Copilot features from some Windows users. Microsoft has a workaround, not a fix.
Key points
- Microsoft is still investigating why Copilot and Copilot Chat buttons disappear in classic Outlook for Windows after upgrading to build 20026.20182 or later.
- Only customers with a Copilot Chat (Basic) licence or a paid Microsoft 365 Copilot subscription are affected.
- The temporary fix is to switch on "Show Apps in Outlook" under File, Options, Advanced.
- A separate Outlook crash bug has been confirmed on machines running Kaspersky Antivirus, tied to a Kaspersky component called mcou.dll.
- Copilot still works in Outlook on the web and in the standalone Microsoft 365 Copilot app while the desktop bug is investigated.
Microsoft is still hunting the cause of a bug that quietly removes the Copilot buttons from classic Outlook on Windows, with no permanent fix in sight.
The issue, first reported by BleepingComputer, hits only people who are actually paying for the feature: users on a Copilot Chat (Basic) licence or a full Microsoft 365 Copilot subscription. Buttons that should sit above the ribbon and in the side navigation simply aren't there. It's a pattern we've seen before with this client: our 3 September story on ARM crash failures was the third Outlook stability report we filed in a fortnight.
My read: this isn't a security hole, but it's a neat illustration of how fragile a paid AI feature can be when it rides on top of a thirty-year-old mail client. Customers are paying a premium and getting a support article.
What exactly is broken?
After upgrading classic Outlook for Windows to build 20026.20182 or higher, Copilot entry points can vanish from the interface. The feature is still licensed; it just has nowhere to click.
Affected users may see any of these symptoms:
| Symptom | Where it shows up |
|---|---|
| Copilot button missing | Top-right, above the ribbon |
| Copilot icon missing | Left app bar or More Apps area |
| "Open" does nothing | Add Apps menu |
| Command greyed out | Ribbon customisation |
Microsoft's engineers have traced it to a plumbing problem inside Outlook's profile system. Outlook, they say, "is unable to locate the MAPI property PR_PROFILE_USER_SMTP_EMAIL_ADDRESS_W within the null profile section."
Outlook stores account details in a small internal database called a profile. Copilot needs to read your email address from it to activate. On affected machines that address isn't where Copilot expects it, so the button never loads.
Is there a workaround?
Yes, and it takes about ten seconds. Open classic Outlook, click File, then Options, then Advanced. Under "Outlook panes," tick "Show Apps in Outlook."
The buttons should return. If they don't, Microsoft suggests creating a fresh Outlook profile, or switching to the new Outlook client or Outlook on the web, neither of which is affected. This is a cosmetic issue for a paid feature; the underlying data is untouched.
What about the Kaspersky crashes?
Separately, Microsoft has confirmed a second, unrelated bug: classic Outlook is crashing on machines running Kaspersky Antivirus. The crashes log an "Event 1000" entry in Windows and point at mcou.dll, the Kaspersky Mail Checker component.
Microsoft's Outlook team is still investigating and, for now, is directing Kaspersky customers to contact Kaspersky's own support.
Should ordinary users worry?
No. Neither bug leaks email or lets anyone in. The Copilot glitch is an annoyance for paying customers; the Kaspersky crash is more disruptive but still a stability problem, not a break-in.
If your Copilot buttons have vanished, try the setting above before opening a ticket. Running Kaspersky and seeing crashes? That's now a known combination, and your antivirus vendor is the right first call.
Watch whether Microsoft ships a proper profile-handling fix in the next monthly Outlook update, or whether the workaround quietly becomes the permanent answer.
