A modern CPU can be pushed hard by typing an email in Outlook? Welcome to another Microsoft bug

Another very strange bug, this time in classic Outlook for Microsoft 365 users, means that just typing words in an email can spike your CPU activity.

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Darren Allan

Tech Reporter

Published Apr 15, 2025 10:45 AM CDT

2 minutes read time

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TL;DR: Microsoft has identified a bug affecting some Microsoft 365 users, which spikes CPU usage to the tune of up to 50% when typing emails in the Outlook classic app. This issue affects users on the Current and Monthly Enterprise channels (as well as testers) who are using version 2406 Build 17726.20126 (or later). Microsoft is investigating the problem which is a pretty baffling one.

Microsoft has confirmed that there's a bug in Outlook for Microsoft 365 - the classic version of the email app, that is - and it's an odd one that can ramp up the workload on your CPU.

Merely typing letters in an email should not be stressing your processor (Image Credit: Pixabay)

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Yes, for some business users, just typing an email message in classic Outlook can cause their processor fan to suddenly kick up a notch and spin faster to cope with a 30% to 50% usage spike, as Microsoft describes it.

Commonly users report around the lower end of that spike, but still, it's pretty alarming to have this happening when just typing some letters on your keyboard.

As Microsoft points out in a support document (noticed by Neowin), this is quite easily observable, as you can pop up Task Manager is a small window and watch the CPU activity as you start to type in Outlook. It'll shoot up, and then when you stop typing, it'll calm back down again.

This very odd bug - and we're seeing more than a few of these from Microsoft of late - is affecting those on the classic version of Outlook after updating to version 2406 Build 17726.20126 (or later, that version was out in June 2024). It's happening on the Current channel, testing channels, and Monthly Enterprise channel.

So, it seems that this issue has been hanging around for a while, and there are reports of it being a problem in November 2024.

Microsoft is investigating and there's no fix yet, but the company does provide a workaround: switch to the Semi Annual Channel using the Office Deployment Tool or via a Registry edit. Apparently, that channel has managed to avoid whatever's causing this glitch.

Alternatively, the low-tech fudge that some folks have been using is simply typing messages in a word processor and then copying and pasting them over to the email in Outlook.

Hopefully this is an issue Microsoft will have fixed soon enough.