If you use Outlook 2002 or XP then you should find this tip quite useful if you send a lot of emails.
When you type an address into the To:, Cc: or Bcc: lines of a new message in Outlook 2002 or XP, Outlook will use a feature called AutoComplete and automatically suggest a addresses based on addresses it that it has cached.
This can be useful but it can also be a pain if an address that you use regularly appears at the bottom of the list thanks to address that you don't use very often. Don't worry, help is at hand:
If you want to turn off this feature and not have addresses are suggested, click on the Tools menu, choose Options, then click the "E-Mail Options" button, and the "Advanced E-mail Options" button. Uncheck the box for "Suggest names while completing the To, Cc and Bcc fields". It won't bother you again.
However, you might find that a little drastic. To remove one address from the list, open a new message and begin typing in the address then use the up and down arrow keys to select the address that you want removed from the addresses suggested list. When the address you no longer want is highlighted, press the DELETE key.
If you want you can also remove all the saved addresses. To do this delete the file with the ".nk2" extension normally located in Application Data/Microsoft/Outlook folder for each Outlook profile. Do not try to edit this file as you will more than likely corrupt it and this can lead to instabilities in Outlook.
Choose the options that suits the way you work best.