Outlook : How to Delete the Entire History Autocomplete name list in outlook ?

When you start typing the person's email address, you will see it pop up it's suggestion for auto-complete. Just press the delete (DEL) key on your keyboard. The entry won't be suggested again, until the next time you send a message to it.

If more than one suggestion is listed, you can use the up/down arrow keys on your keyboard to highlight the one you want to remove from the suggestion list. Then press DEL.

Again, this removes the suggestion, but doesn't disable the auto-complete feature from adding it back into it's suggestion database at a later time if you send an email to that person again. To clear all entries and disable the feature completely, see the link that splash provided. There may be other methods as well, but none come to mind.

How to Delete the Entire History List File

If you find too many of the addresses in the history are malformed or you wish to move a history list from one computer to another, you can find the file in the following location: C:\Documents and Settings\username\Application Data\Microsoft\Outlook\<profile_name>.NK2
You will have to have hidden files and folders disabled in folder options to see the application data folder.

How to Remove Individual Names from History List

1.    Begin typing the name of the name you wish to remove in the Outlook TO: Field in a new message.

2.    Use the arrow key (not the mouse) to select the incorrect name.

3.    Hit the Delete key (not Back Space). This will remove the name from the history list.

How to Change the Maximum Names in the History List

1.    Click Start and Run. Type regedit, and then click OK.

2.    Find the key: H_KEY_CURRENT_USER\Software\microsoft\Office\10.0\outlook\

3.    In the right pane, right-click and select New, then DWORD Value. Name it: MaxNicknames.

4.    Double-click on the key and type the number of entries (in the value box) you wish to have as the maximum. The Default is 1000.