Every time you send an eMail outlook stores the address you sent to in a hidden auto complete file that ends in “.nk2”.  This document will give you the resources to back up this file, move it to a new computer, edit the file. It is important to mention that if you just want to remove a bad address you do not need to read the rest of this document.  Simply start to type the bad eMail address from the to box in a new eMail, when it is displayed, arrow to it and press the delete key on your keyboard. If you are looking for a FREE tool to modify the file it can be found here. The nk2 file is located in the following folder  (Replace the “user name” with yourown)… XP:  \Documents and Settings\user name\Application Data\Microsoft\Outlook (Other) WinVista/Win7/Win8: \Users\user name\AppData\Roaming\Microsoft\Outlook You can try to click here to open the folder. For the detailed Microsoft directions on how to backup the file go here.