Even after you have corrected a wrong email address in your contacts, the old email will continue to bug you when outlook tries to autocomplete addresses for you.
Microsoft outlook stores any email address you type into the “To” field–wrong or right. For example, if I type in “email@example.com” instead of “firstname.lastname@example.org”, outlook will try to autocomplete the erroneous address into the email field. No matter where you try to correct this, the error email address will always be remembered.
Likewise, the bigger the cache of email addresses gets, the slower and more useless it becomes.
If you are lucky enough to trigger the autocompletion box, you can press the down arrow until the error email address is selected and then hit DELETE. Often, however, the autocompletion box will not be displayed. Microsoft has a work-around.
The easiest thing to do is to blitz the whole file. The file lives here where your-profile is unique to your installation: “C:\Documents and Settings\your-profile\Application Data\Microsoft\Outlook”
Delete or rename all *.nk2 files at this location.
If you need a detailed, walk-through you can find it here: