There is only one file type that uses the .OBI extension:
Outlook RSS Subscription File
File created by Microsoft Outlook, a calendar and email program; contains RSS subscription names and properties in an XML format; used to store RSS feed subscriptions for an outlook profile.
OBI files are named using the convention <profilename>.sharing.xml.obi. They are typically located in the following user directory:
OBI files can be exported to Outline Processor Markup Language (.OPML) files by selecting the following option in Outlook:.
Updated: September 28, 2009