[更新検知] https://techcommunity.microsoft.com/blog/exchange/exchange-servers-may-become-unstable-after-installation-of-october-2026-windows-/4565382 #427

更新対象

• 原文 URL: https://techcommunity.microsoft.com/blog/exchange/exchange-servers-may-become-unstable-after-installation-of-october-2026-windows-/4565382

原文の変更箇所 (自動生成された diff。ヒントであり全てではない)

[Removed or original paragraph]

• [highlight]Update October 20, 2026: Added a FAQ to this post.[/highlight]
• Since October 13, 2026 (Microsoft “Patch Tuesday” release cycle), we have seen some reports of customer issues where Exchange Servers become unstable after a set of October updates are installed.
• Issues reported are not related to installation of October 2026 security updates for Exchange Server (https://techcommunity.microsoft.com/blog/exchange/released-october-2026-exchange-server-security-updates/4563014). This is not a “known issue” related to October 2026 Exchange update. Any version of Exchange that runs on impacted versions of Windows could be impacted.
• [highlight]Not all Exchange servers will be impacted by installation of those updates equally; the severity and speed of impact varies based on Exchange server load. Some servers might never see a problem.[/highlight]
• Do not uninstall October 2026 Windows Server updates.
• From an elevated Command Prompt on an Exchange Server, run:
• reg add "HKLM\SOFTWARE\Microsoft\Rpc" /v EpmapSavedContextCap /t REG_DWORD /d 65536 /f
• Reboot the server.
• After the reboot, monitor the environment and confirm whether the issue recurs. If it re-occurs, raise the limit (we have so far not seen any cases where this might be needed). This has been shown to solve the problem based on customer reported cases that we have assisted to date.
• More information can be found in Users might be unable to sign in to OWA or send emails on Exchange Server (https://learn.microsoft.com/en-us/windows/release-health/status-windows-server-2025#5047msgdesc) (Windows Server known issues and notifications).
• Should we wait for updated set of Windows updates or wait for next month’s Windows updates release? Should we uninstall Windows Server updates? No, you should install already released Windows updates as soon as possible. October 2026 updates for Windows Server carry a significant security payload and installation of those updates should not be delayed for the sake of a single issue with Exchange server interoperability. Follow the recommendation in this blog post.
• Can the mentioned Windows registry setting be created before we install October 2026 Windows Server updates on our Exchange servers? Yes. Creating the registry key beforehand has no impact on Windows Server because the registry key is read and used only once October 2026 Windows Server updates are installed. The registry key remains intact during update installation.
• Is there another fix coming? From Exchange? From Windows? When? Should we wait for it? There is no imminent follow-up release from either Windows or Exchange. Both teams are still analyzing this long-term. Future improvements in the area are possible. You should not wait for a new release; please install October 2026 Windows Server updates and follow Exchange server recommendation in this post.

[Added or updated paragraph]

• [highlight]Update November 10, 2026: This blog post has been updated to reflect that the solution for issues mentioned is to install November 2026 (or later) updates for Windows Server that your Exchange Server is running on.[/highlight]
• After October 13, 2026 (Microsoft “Patch Tuesday” release cycle), we have seen some reports of customer issues where Exchange Servers become unstable after a set of October updates are installed.
• Issues reported are not related to installation of any version of Exchange Server updates. Any version of Exchange that runs on impacted versions of Windows could be impacted.
• Please install November 2026 (or newer) updates for Windows Server. Customers who have previously created the EpmapSavedContextCap registry key to address the issue in October can leave the registry key in place, but the key is not required once November 2026 Windows Server updates are installed.
• Should we wait for updated set of Windows updates or wait for next month’s Windows updates release? Should we uninstall Windows Server updates? Windows Server has released an update that addresses this issue in November 2026. Please install that.
• Can the mentioned Windows registry setting (that was used as a workaround) be created before we install October 2026 Windows Server updates on our Exchange servers? Yes. Creating the registry key beforehand has no impact on Windows Server because the registry key is read and used only once October 2026 Windows Server updates are installed. The registry key remains intact during update installation. Also note that after November 2026 Windows Server update is installed, the registry key / workaround is no longer required.
• Is there another fix coming? From Exchange? From Windows? When? Should we wait for it? Windows Server has released an update that addresses this issue in November 2026. Please install that.
• November 10, 2026: Updated the post to reflect that November 2026 Windows Server updates should be installed to address this.

作業内容

この Issue が GitHub Copilot cloud agent に割り当てられた場合は、次の手順で対応してください。

1. 原文 URL のスラッグから日本語記事のファイル名を推測し、見つからない場合は抄訳記事冒頭の注釈内の URL を検索して対象記事を特定する
2. 原文を取得し、diff をヒントとしつつ原文全体と日本語記事全体を広く比較して変更箇所を洗い出す (diff に現れない変更も見落とさない)
3. リポジトリの .github/copilot-instructions.md と .github/agents/update-translated-blog-post.agent.md に従う
4. 修正が完了し、Hexo のビルドが成功することを確認したうえで、Draft PR を作成する