Outlook doesn't display zip files in the Insert file dialog

Problem: When you open the Insert File dialog in when composing an email message, Outlook "hides" the zip files in the directory. The only way to add a zip as an attachment to a message is by opening Windows Explorer and dragging the file to the message window.

Cause: Windows has a system component that treats zip files like ordinary file folders and Outlook sees these files as folders. In most cases, it only happens when you don't have third party compression programs installed, so you may see the behavior on one system but not another.

Reasoning: Under certain conditions, the Windows shell will include a folder attribute for zip files. This result is cached, thus Outlook will exhibit the same behavior throughout the session.

Solution: Restart Outlook or if it happens often, Disable Compressed folders. If you use a third party program (such as WinZip) you can leave compressed folders disabled. Note that disabling compressed folders will also disable XP searching in ZIP files when searching for files.

To disable the feature at the Start menu, Run command, type:

regsvr32 /u zipfldr.dll
regsvr32 /u cabview.dll

To restore the functionality, return to Start Menu, Run command and type:

regsvr32 zipfldr.dll
regsvr32 cabview.dll