Introduction

Microsoft's classic Outlook client has recently been identified as a source of significant CPU usage spikes, particularly during email composition. This issue has affected users across various Windows versions, leading to performance degradation and increased power consumption. This article delves into the background, technical details, implications, and solutions related to this problem, providing IT professionals with the necessary information to address and mitigate the issue effectively.

Background

In April 2025, Microsoft acknowledged a bug in the classic Outlook for Windows that causes CPU usage to spike between 30% and 50% when users type emails. This problem was observed after updating to Version 2406 Build 17726.20126 and later on the Current Channel, Monthly Enterprise Channel, and Insider channels. Users reported noticeable slowdowns and increased power consumption during email composition. (support.microsoft.com)

Technical Details

The issue manifests as significant CPU usage spikes during the typing of emails in Outlook. Users have reported that disabling spell-check options and add-ins did not resolve the problem. The bug appears to be linked to how Outlook handles text input fields, leading to increased processor utilization and power consumption. (bleepingcomputer.com)

Implications and Impact

For organizations relying on Outlook for daily communications, this bug can lead to:

  • Reduced System Performance: High CPU usage can slow down other applications and overall system responsiveness.
  • Increased Power Consumption: Elevated CPU activity leads to higher energy usage, which is particularly concerning for laptop users due to reduced battery life.
  • User Frustration: Persistent performance issues can decrease productivity and user satisfaction.

Microsoft's Response and Solutions

Microsoft has acknowledged the issue and is actively working on a fix. The company plans to roll out updates across different channels as follows:

  • Beta Channel: Version 2505 Build 18822.15000 – Early May 2025
  • Current Channel Preview: Version 2505 Build 18827.20000 – Mid May 2025
  • Current Channel: Version 2505 Build 18827.20000 – Late May 2025

In the interim, Microsoft recommends switching to the Semi-Annual Channel, where the issue has not been observed. This can be achieved by adding a specific registry key or using the Office Deployment Tool. (support.microsoft.com)

Workaround Steps

To switch to the Semi-Annual Channel using the registry method:

  1. Open Command Prompt as Administrator:
  • Press INLINECODE0 and select "Command Prompt (Admin)".
  1. Enter the Following Command:

``INLINECODE1 `INLINECODE2 FileINLINECODE3 Office AccountINLINECODE4 Update OptionsINLINECODE5 Update Now`.

This process will switch your Office installation to the Semi-Annual Channel, potentially mitigating the CPU spike issue. (support.microsoft.com)

Conclusion

The CPU spike issue in Microsoft's classic Outlook client poses significant challenges for users and IT professionals. While Microsoft is actively working on a permanent fix, understanding the problem's background, technical details, and available workarounds is crucial for maintaining system performance and user productivity. IT departments should consider implementing the recommended temporary solutions and stay informed about upcoming updates to ensure a smooth transition once the fix is deployed.