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How to Fix “Unable to Open Outlook Attachment” Error – Quick Solutions Inside

Ritu Roy | fix How to's Outlook outlook error Software Technology | 5 minutes read | Modified on: 16-07-2025
Unable to Open Outlook Attachment

Many Microsoft Outlook users face a frustrating issue where they’re unable to access email attachments. When attempting to open an attachment, either by double-clicking it or by using the right-click > Save As option, the action fails. Instead of opening the file, Outlook displays an error message: “Unable to open Outlook Attachment.”

Even basic troubleshooting methods like restarting Outlook or rebooting the system don’t resolve the problem. The attachments remain inaccessible no matter what. So, what’s the next step?

Don’t worry, this blog will guide you through effective solutions to fix the Outlook attachment opening issue and get things working again.

Common Reasons Behind the “Unable to Open Outlook Attachment” Error

Several factors can lead to this issue in Microsoft Outlook. Below are the most common causes:

  • Restricted Access to Temporary Internet Files and Folders- If a user is restricted from accessing the temporary Internet files or folders either on the local system or a server, Outlook may fail to open attachments.
  • Storage Limit Reached in Temporary Folders – Outlook stores temporary copies of attachments in a hidden subfolder. When this folder reaches its storage limit, new attachments cannot be opened or saved, leading to the error.
  • Outlook Security Restrictions – Outlook may block attachments it deems potentially harmful. Due to built-in security protocols, suspicious files are locked to protect your mailbox and system from possible threats, resulting in access errors.
  • Corrupt or Inaccessible PST File – If your Outlook data file (PST) is damaged or inaccessible, it can prevent attachments from opening properly.
  • Repeated Access to the Same Attachment – When the same attachment is accessed multiple times, Outlook creates duplicate temporary files with the same name. Eventually, it hits a limit and fails to generate another temp file, preventing further access.
  • Blocked File Extensions in Outlook Web App (OWA) – If you’re using Outlook through Office 365 or Outlook Web App, certain file types may be automatically blocked for security reasons. Attachments with restricted extensions will not open or download.

Solutions to Fix the “Unable to Open Outlook Attachment” Error

If you’re encountering an error while trying to open attachments in Microsoft Outlook, don’t worry, there are proven solutions that can help. Below are two detailed methods based on the root cause of the issue.

Solution I: Fix When the Error Is Caused by Temporary Internet Files

Outlook stores attachments in a hidden temporary folder. When this folder becomes too full, it may prevent attachments from opening. Follow the steps below to clear it:

Steps to Clear Outlook’s Temporary Folder:

  1. Open the Run dialog: Press Windows + R, or click Start > Search for Run.
  2. Access the Registry Editor: Type regedit.exe and click OK.
  3. Find the Outlook Temp Folder Path:
    • In the Registry Editor, click on Edit > Find.
    • Type OutlookSecureTempFolder and click Find Next.
  4. Note the Folder Location:
    • Once found, double-click the key on the right panel.
    • Copy the full folder path displayed in the key value.
  5. Navigate to the Folder:
    • Open Run again (Windows + R), paste the copied location, and press OK.
  6. Delete Temporary Files:
    • The folder will open in File Explorer.
    • Select and delete all files inside the folder.
  7. Restart Outlook:
    Now, try opening the attachments again—Outlook should allow access.

Tip: If the issue persists, try disabling Outlook add-ins, as some third-party add-ins may interfere with attachment handling.

Solution II: Fix When the Error Is Caused by Outlook Security Protocols

Outlook may block attachments due to its built-in security settings. Modifying registry keys can help lift unnecessary restrictions. Follow the instructions based on your Windows version.

For Windows XP (Older Versions):

  1. Click Start > Run, type sysrestore and press OK.
  2. On the “Welcome to System Restore” page, select Create a restore point, and click Next.
  3. Enter a name for the restore point and click Create > Close.
  4. Repeat Steps 1–3.
  5. This time, select Restore my computer to an earlier time, and click Next.
  6. Choose a restore point (e.g., “Guided Help – Registry Backup”), and click Next.
  7. Confirm the restore operation by clicking Next, and then OK.

This creates a backup before editing any registry settings, ensuring you can roll back in case of an error.

For Windows 10 (Latest Versions):

  1. Press Windows + R, type regedit.exe, and hit Enter.
  2. If prompted for admin access, enter your administrator password.
  3. In the Registry Editor, navigate to the registry key you want to modify.
  4. Click on File > Export to create a backup.
  5. Choose a location to save the backup, provide a filename, and click Save.

After backing up the registry, proceed with modifying the required keys based on Microsoft’s official instructions for your specific Outlook security settings.

Solution III: When Outlook Web App (OWA) Doesn’t Open Attachments

If you’re using Outlook Web App (OWA) and are unable to download or open attachments with certain file extensions, the issue is likely due to security policies that restrict specific file types.

Why This Happens:

OWA is configured to block attachments that may pose a security risk, such as .exe, .bat, or .js files. These restrictions are set by default in Exchange Server policies.

What You Can Do:

To resolve this, you’ll need to modify the policy settings that control file extension permissions.

Recommended Action:
Contact your Exchange Administrator and request to:

  • Remove the blocked file extension from the restricted list.
  • Add the extension to the list of allowed file types for OWA.

This change can only be made on the server level by someone with the proper administrative rights.

Conclusion

In this blog, we covered one of the common issues faced by Outlook users, the “Unable to Open Attachment” error. We discussed:

  • The main causes behind the problem such as temp folder limits, security restrictions, or PST corruption.
  • Three detailed solutions tailored to each scenario:
    • Cleaning up temporary Internet files.
    • Editing registry settings to remove security restrictions.
    • Adjusting OWA policies for blocked attachments.

If you’ve tried all the above fixes and still can’t open attachments, the issue may lie in a corrupt or damaged PST file.

Final Recommendation: Download and install CubexSoft Outlook PST Converter Tool to scan and convert your PST file. The tool offers an intuitive interface and guided steps to restore access to all your emails, attachments, contacts, and more. It supports various file formats such as PDF, MBOX, EML, MSG, DOC, CSV, Office 365, Gmail, and many more.