Outlook Classic update breaks Copilot for some users
Users on Version 2605 (Build 20026.20076) report Copilot errors in the classic Outlook desktop client. The same features reportedly worked in Version 2604 (Build 16.0.19929.20172). The problem appeared after the May 2026 Current Channel rollout. Error messages vary, but the reports describe Copilot failing inside classic Outlook rather than a broader Microsoft 365 outage. Microsoft has not yet published a confirmed fix or workaround for this specific build issue.
Classic Outlook is still the fallback for many people who dislike the new Outlook experience or depend on older add-ins. Until now, that fallback could feel like the safer choice while testing Copilot gradually. This report is a reminder that classic does not automatically mean stable once Copilot is involved. If Copilot is part of your daily email triage, a client update can break the workflow even when the rest of Outlook still opens normally.
Analysis
If Copilot matters to your inbox routine, note your Outlook build before updating and keep one fallback path ready, such as Outlook on the web or new Outlook. Do not move a whole team off classic Outlook because of one community report, but do pause any forced update plan until you have tested the build on a small group.
Citation
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