Outlook buy default saves all the address which we send on first time. Which can be seen when u sends mail to same person again?
For example: I send a mail to firstname.lastname@example.org. for the first time I will type the address in to address. When I like to send a message again to the same address, just pressing "micro" u will get the remaining in the drop down list as shown in figure.
Real fact is this a buffer file which does not save in ur outlook contacts. Which is saved in ur profile path: drive:\Documents and Settings\user name\Application Data\Microsoft\Outlook. With the extension NK2
Which must be taken while u format or freshly install ur OS
For more Details of outlook nk2