Microsoft says it will soon fix a known issue causing CPU spikes when typing messages in recent versions of its classic Outlook email client.
Redmond confirmed this bug last week after a wave of user reports on various online platforms since early November, including Microsoft’s community website, with those affected saying that disabling all spell-check options and add-ins did not resolve the CPU usage issues.
As the company says in an update to the original support document, this issue now impacts users in the Semi-Annual Channel who have updated to Outlook Version 2406 Build 17726.20126 and later.
“When you write an email in classic Outlook for Windows, you may notice the CPU spikes up to 30 to 50% at some times and increases the power consumption. You can observe this if Task Manager is open while you type,” the company said.
“We found that the issue now occurs in Semi Annual Channel. If you urgently need to work around the issue the only option would be to revert to Version 2405. This is not recommended since there have been security updates since that version.”
Microsoft says the fix will roll out starting in early May to affected users who install the following builds:
Outlook users who have to mitigate this issue until then can revert to Version 2405 as a temporary workaround using the following steps:
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Locate the build of Version 2405 for the respective channel you are on from the Update history for Microsoft 365 Apps (listed by date) – Office release notes.
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Open a Command Prompt (Run as Administrator).
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Type or paste the command below (replacing the build from Step 1), and then press Enter:
"%programfiles%\Common Files\Microsoft Shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.17628.20144
As an alternative method, Microsoft also provides the Office Deployment Tool to revert to earlier versions of Office.
Recently, the company has also released emergency Office 2016 updates to fix crashes in Word, Excel, and Outlook caused by the April 2025 security updates.
Previously, it addressed multiple other Microsoft 365 and Office issues, including a bug that triggered Outlook crasheswhen clicking a button that should’ve helped users switch back to classic Outlook and a widespread licensing issue blocking access to Microsoft 365 services for some customers with Family subscriptions.
It also resolved a known issue that broke Outlook email drag-and-drop after installing recent updates on Windows 24H2 systems and a bug causing Outlook to crash when writing, replying to, or forwarding emails.
