I'm not sure why this happens, but Outlook creates copies of the same attachment in AppData when I open the attachment externally on subsequent visits.

Steps to recreate this behavior

  • Example email contains attachment abc.pdf
  • Open PDF with system viewer for the first time, saved in AppData/.../Content.Outlook/.../abc.pdf
  • Close the email, then reopen the email (no need to close the attachment or Outlook)
  • Reopen the PDF with system viewer
  • PDF now saved in AppData/.../Content.Outlook/.../abc (002).pdf.
  • Subsequent opens of the attachment will save to abc (003).pdf, abc (004).pdf, etc.


  • Is there a reason for Outlook to behave in this way?
  • Is there a way to deactivate this redundant file proliferation?
  • If not, is there an easy way to clean up the duplicate files created?

An official answer by a Microsoft support engineer says this :

When you open attachments on email directly from Outlook, a copy is written to a temporary folder on your hard drive so your virus scanner can check it before it is opened. The folder Outlook writes this temp file to is under the Temporary Internet Files folder where IE writes pages to when you surf the internet. This offers more security as only your user account and the computer administrator account can view the files under this folder. The only way to avoid “losing” attachments in this well hidden folder is to save them to your hard drive, before opening.

So this behavior is by design and is supposed to protect you against "losing" attachments. There is no way for you to stop it happening.

The most that I see you can do is periodically clean out this folder. You could do it manually, or it may be simpler to use the application OutlookTempCleaner.

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  • Instead of using a third-party tool, Storage Sense and/or Disk Cleanup, will remove the files in the folder in question. – Ramhound Oct 23 '18 at 17:10
  • @Ramhound I just tried Disk Cleanup and it did not remove the duplicate files from the AppData folder – Zaid Oct 25 '18 at 6:27

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