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TROUBLESHOOTING NOTE

Outlook 2024/2021 LTSC crashes when opening email from Viva Engage and similar services

ResolvedSources checked: 2026-09-054 stepsFaultNote editorial team

What to do first

Update the affected LTSC product to Microsoft's fixed build or later, then confirm that opening the affected message no longer crashes Outlook.

Affected products and symptoms

Product
Classic Outlook for Windows
Versions and conditions
Outlook 2024 LTSC around 16.0.17932.20700 and Outlook 2021 LTSC around 16.0.14334.20440; fixed in 2024 LTSC 17932.20766 and 2021 LTSC 14334.20662
Error codes and identifiers
Event 10000xc0000005

Symptoms

  • Classic Outlook crashes when opening email sent by Viva Engage, Viva Insights, Yammer, Power Automate, or similar services
  • Windows Event Viewer records Event 1000 for OUTLOOK.EXE with exception code 0xc0000005

Causes and conditions

Microsoft confirmed a crash when affected messages are opened in specified LTSC builds, but its public article does not explain the internal cause.

Before you start

  • Record the product name and build under File > Office Account
  • Save Event 1000 and the exception code from Event Viewer
  • Save unsent messages and close Outlook

Precautions

  • The fixed build differs between LTSC 2024 and LTSC 2021
  • Do not bypass the organization's update policy by installing an external package

Tools and official pages used in this guide

Classic Outlook for Windows troubleshooting sequence: Confirm applicability; Run Office Update; Confirm the build; Test an affected message
Procedure overview created by FaultNote. Read the precautions and full instructions before changing settings. Read the full steps

Step-by-step instructions

  1. 01

    Confirm applicability

    #

    Confirm that this is Classic Outlook LTSC 2024 or 2021 near the listed older builds. This issue does not apply to new Outlook.

    If Classic Outlook opens, record the product name and version under File > Office Account. If it does not open, run the specified command from Win+R and confirm that it is not being confused with new Outlook.

  2. 02

    Run Office Update

    #

    Choose File > Office Account > Update Options > Update Now. On an organization-managed device where this is unavailable, ask the administrator.

    An organization may manage the mail server and update channel. Do not delete PST/OST files or profiles; compare whether the same mailbox opens in Outlook on the web to distinguish a service problem.

    Official links for this step

    Check before continuing

    The official Microsoft known-issue update guidance or signed package opens, and its product, OS, and version requirements match this computer.

  3. 03

    Confirm the build

    #

    Confirm version 17932.20766 or later for 2024 LTSC, or 14334.20662 or later for 2021 LTSC.

    After changing settings, fully exit Outlook, confirm in Task Manager that OUTLOOK.EXE is no longer running, and start normally. Restore add-ins one at a time and record which change makes the symptom return.

  4. 04

    Test an affected message

    #

    Restart Outlook and open a message from a known affected sender to confirm that Outlook does not crash.

    Use a small message to yourself to verify sending, receiving, and body display. Retain the old profile and data files until required mail, signatures, and shared mailboxes have been checked.

    Completion criteria: a fixed or later build is displayed and Event 1000/0xc0000005 is not logged again. If unmet, do not repeat the same operation; follow the next branch: if the update is not offered, ask the Microsoft 365 administrator to check the update channel and deployment status.

    Check before continuing

    Decision: restart Outlook and open a message from a known affected sender. Test sending, receiving, and body display with a small message to yourself, and retain old profiles and data until necessary content is verified.

Check the result

  • A fixed or later build is displayed
  • Event 1000/0xc0000005 is not logged again

If the problem continues

  • If the update is not offered, ask the Microsoft 365 administrator to check the update channel and deployment status
  • Until it is applied, view affected messages in Outlook on the web

Fix status

Resolved — Microsoft provided an initial fix in the March 10, 2026 public update and identifies 2024 LTSC 17932.20766 and 2021 LTSC 14334.20662 as the final fixed builds in the May 12, 2026 public updates.

Frequently asked questions

Is new Outlook affected?

This article applies to specified builds of Classic Outlook LTSC products.

Official sources and dates

Source publication or resolution date: 2026-05-01. Sources checked: 2026-09-05. The check date is not the date the problem first occurred. Interface labels can vary between versions and display languages.

Related troubleshooting guides

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