There is only one file type that uses the .OSS extension:
Microsoft Outlook Saved Search File
Search file saved by Microsoft Outlook, an email and calendar program included with Microsoft Office; contains email search criteria for a virtual folder; used for filtering email into virtual email folders that match specific search parameters.
Saved searches can be used as an alternative to manually moving or copying email messages. Since Outlook constructs saved search virtual folders on-the-fly, the program does not actually make copies of the matching criteria. Instead, it only filters the email messages.
Updated: February 18, 2010