Outlook itself uses two contact systems, you have one where you manage everything. And there is another list that Outlook manages itself, in that list, everybody you have been in contact with gets automatically added.
Getting a list of everybody you have ever been in contact with can become a “bit” irritating after a while, but there is luckily two easy ways to clean up that list:
1) Remove just specific contacts
#1: Create a new mail message
#2: Start typing the name of the contact to remove
#3: Use the up/down arrow keys until you have selected the contact
#4: Press delete
2) Removing all auto-added contacts
Locate and simply delete all Outlook`s .nk2 files, normally located under “C:Documents and Settingsyour-profileApplication DataMicrosoftOutlook”.