1) It is stored in your main pst-file if you accept the default location. To
see the location of your default pst-file choose;
File-> Data File Management...
2) You can simply delete the folder in Outlook where the RSS items come in
for that feed. This will automatically unsubscribe you from this feed as
well.
If you only wish to delete some old RSS items see;
http://www.msoutlook.info/question/312
3) Usually an RSS feed does not take up a whole lot of space and Outlook
also automatically returns white space from the mail database (pst-file)
when it contains more than 5% of white space and when the computer is idle.
If you directly want to return the unused space in the pst-file to Windows,
empty your Deleted Items folder and run the Compact Now command on the
pst-file.
For more details see:
http://www.msoutlook.info/question/81
