[German]Users of Microsoft Outlook Classic have been plagued for months by CPU load spikes when typing texts. Microsoft has now acknowledged this problem with Office 365 (from version 2406, build 17726.20126).
Users of Microsoft's Outlook Classic are used to bugs. Among other things, there is always the effect that the program becomes quite slow and reacts sluggishly when typing. German blog reader Viebrix pointed out the issue in a comment and wrote: "The slow behavior of Outlook [classic] when typing (which I mentioned here some time ago and jokingly associated with a reading/learning AI) has now finally been noticed by Microsoft. The problem appears in the Classic version in the newer versions.
Microsoft confirms CPU spikes
Microsoft published the support article CPU spikes when typing in classic Outlook for Windows on April 14, 2025, in which a problem with the classic version of Outlook 365 is confirmed. Microsoft describes the problem as: When typing a simple email in the classic version of Outlook for Windows, users may experience a 30-50% spike in CPU usage at certain times, increasing power consumption. Users can observe this effect by opening the Task Manager in parallel and observing the CPU load while typing.
According to Microsoft, this issue may occur after updating to version 2406 build 17726.20126 and later in the Current Channel, Monthly Enterprise Channel or Insider Channels. The Outlook team is currently investigating this problem, as a cause is probably still unknown.
What is the remedy?
Well, the most simple solution is: Use Thunderbird. And also the effect shouldn't occur in the Office packages with perpetual licenses (Office 2019, 2021, 2024) either. Only the "broken" Office 365 builds in the Current or Monthly channel show the error.
Microsoft officially recommends switching to the semi-annual channel, where the problem has not been observed. It's a popular strategy in the Microsoft universe to switch to a software version where a bug has not yet been observed. The support article also describes methods for switching to the semi-annual channel. The alternative that Viebrix suggested in his comment is to downgrade Office 365 to a build prior to version 2406 build 17726.20126. Question: Is anyone affected by this issue?
Having the issue here, on OL 2502 build 18526.20264. It doesn't reach 30% but is clearly pinning at least one CPU core. Once it does that, it often stays there even if you stop typing. As soon as you focus on a different app window, it drops off from the top of the CPU usage sorting. Alt-tab back, start typing, it jumps up again.