New Outlook Issue — Unable to Open Email Attachments (New Outlook)

Catherine Salgado 115 Reputation points
2026-10-28T13:05:41.0266667+00:00

Reporting a new issue in New Outlook:

When an email is received with an attachment (PDF, Excel, etc.), double-clicking the attachment to open it fails with a "Failed to open — restart Outlook" message. The only workarounds available are to preview the file or download it separately.

Additional details:

  • Double-clicking the email itself can also trigger the same "Failed to open — restart Outlook" error.
  • Restarting New Outlook does not resolve the issue.
  • Switching to Classic Outlook allows the attachment to open normally.
  • Reverting back to New Outlook afterward sometimes works — the attachment opens, but only after an initial "premature fail" message.
  • Continuously switching between Classic and New Outlook to work around this isn't a sustainable solution.

Current workaround: Using Outlook on the Web or Classic Outlook until this is resolved.

Questions for the group:

  1. Does anyone know which recent MS/KB update introduced this issue?
  2. Is there an ETA on a patch or fix from Microsoft?
Outlook | Windows | New Outlook for Windows | For business
Answer accepted by question author
Eugene 100 Reputation points
2026-10-29T06:46:59.6733333+00:00

This fixed for me.

Clear or Create the Olk Cache Folder: Press Windows + R, type %userprofile%\AppData\Local\Microsoft\Olk, check if an Attachments folder exists, create one if it is missing and delete all contents inside Attachments folder. Restart New Outlook.

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  1. Liora 3,285 Reputation points Independent Advisor
    2026-10-29T09:58:05.4033333+00:00

    Hi Catherine,

    Thank you for taking the time to document this issue. I wanted to share an update that may be relevant to everyone following this thread.

    Microsoft has now published Service Health advisory EX1528992 for Exchange Online, which appears to closely match the behavior described here.

    According to the advisory, affected users may:

    • Be unable to open email attachments in New Outlook.
    • Receive a message indicating that the file cannot be opened and that Outlook should be restarted.
    • Find that the "Open" option is no longer available after the error occurs.

    Microsoft has identified the root cause as a recent update to Edge Version 156 that unintentionally enabled an unnecessary configuration, resulting in this behavior.

    Microsoft has already developed and deployed a targeted fix. Based on the latest update, the change may take up to 12 hours to fully propagate across the service infrastructure. Once the fix has reached your environment, users may need to close and reopen New Outlook before the issue is resolved.

    If your organization has access to the Microsoft 365 Admin Center, I would recommend asking your administrator to review advisory EX1528992 in Health > Service health to confirm whether your tenant is affected.

    User's image

    In the meantime, the documented workaround remains to use Save As to download the attachment before opening it, or continue using Classic Outlook or Outlook on the web if those options are currently working in your environment.

    Based on the information Microsoft has published, this now appears to be a known service issue rather than an isolated client configuration problem.

    Thank you again for raising the issue and sharing your troubleshooting results. Hopefully the service-side fix reaches all affected tenants soon and restores normal attachment-opening behavior.

    Kind regards.

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  2. AndrewD.Lawlor 5 Reputation points
    2026-10-28T19:51:34.8733333+00:00

    Hello.

    when I got the first complaint about this issue from a user here, I was still able to open attachments in New Outlook.

    However, last night, I got a WebView2 update to 156.0.4314.5 and now my attachments do not open (same error).

    I was on 155.0.4283.62.

    Someone on github has reported that rolling back his WebView2 seemed to fix the issue with opening attachments in New Outlook.

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  3. Todd Foeckler 0 Reputation points
    2026-10-28T18:55:27.9633333+00:00

    This worked for me:

    • Close New Outlook.
    • Go to Windows Settings > Apps > Installed apps.
    • Locate Outlook (new), click the three-dot menu, and select Advanced options.
    • Click Repair and test the app. If that fails, return to the same menu and select Reset

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  4. AI answer

    2026-10-28T13:06:44.66+00:00

    No Microsoft-published KB or patch ETA currently matches this exact New Outlook error, so continue using Outlook on the Web or Classic Outlook and submit a New Outlook support case with diagnostics while the failure is reproducible.

    Current public status

    • Microsoft’s New Outlook known-issues page does not list the “Failed to open — restart Outlook” failure affecting ordinary attachments or popped-out messages. The attachment issue currently listed concerns attachments deleted through Microsoft Graph API, which is a different scenario. ^1^
    • The public New Outlook release notes contain several nonspecific “various fixes” entries, but no named fix for this exact failure. Therefore, they do not provide a patch date or confirm which release introduced it. ^2^
    • Microsoft’s standard attachment guidance covers file handling, default applications, previews, and saving attachments, but does not document this error as a normal attachment configuration problem. ^3^

    The fact that the same items work in Classic Outlook and Outlook on the Web, while double-clicking either an attachment or the message itself can fail in New Outlook, points to a New Outlook client/session problem rather than a blocked attachment type. It does not, however, identify a specific Windows KB.

    Why a Windows KB might not be identifiable

    New Outlook receives native app builds automatically, generally weekly. Features and some changes can also be delivered through the Microsoft 365 service rather than a conventional Windows KB. It does not use Classic Outlook’s Monthly Enterprise or Semi-Annual update channels. ^4^

    Consequently, uninstalling an unrelated Windows or Classic Outlook update is not supported by the available evidence. In particular, reports involving KB5074109 or KB5077241 concern Classic Outlook startup/hanging, not this New Outlook attachment and message-opening failure.

    Submit the reproducible failure to Microsoft

    Since restarting has already failed, capture diagnostics instead of repeating that workaround:

    1. In New Outlook, select Help → Support.
    2. Select the affected work or school account and accept the privacy statement.
    3. Include:
      • The exact text: “Failed to open — restart Outlook.”
      • That both attachments and double-clicked messages can fail.
      • File types tested, such as PDF and XLSX.
      • Whether preview and download continue to work.
      • That the same message works in Classic Outlook and Outlook on the Web.
      • The approximate date and time of the latest reproduced failure.
      • A screenshot or screen recording.
    4. Reproduce the problem, then select Help → Get Diagnostics → Upload Logs or Send Diagnostics, following the support agent’s instructions.
    5. In Help → Feedback, submit the same report and select Yes under Can we contact you about this feedback? to include diagnostic information. ^5^

    For a managed Microsoft 365 tenant, the administrator should also check Microsoft 365 admin center → Health → Service health and Message center for a tenant-specific advisory. Microsoft identifies Message Center as the source for organization-specific release timing and status. ^4^

    If Help → Support or Feedback is unavailable, the organization may have disabled it by policy; contact the Microsoft 365 administrator to open the support case. Feedback can also be unavailable when optional connected experiences are disabled. ^5^

    Workaround pending investigation

    Continue with either:

    • Outlook on the Web, or
    • Classic Outlook for opening attachments and messages in separate windows.

    Previewing or using the attachment menu to save the file is also valid when appropriate, but continuously switching Outlook clients is not required. There is currently no publicly documented rollback, registry change, or security-setting adjustment for this exact New Outlook failure.

    References

    1. Fixes or workarounds for recent issues in new Outlook for Windows ...
    2. Release notes for Outlook for Windows (new) - Office release notes ...
    3. Troubleshoot attachment problems in Outlook for Windows
    4. Manage updates in new Outlook for Windows
    5. Contact support and provide feedback in new Outlook for Windows | Microsoft Support
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