Microsoft Outlook 2003, 2007, 2010 and 2013 has a feature called Email Address Auto Complete. As you type an email address into the TO:,  CC: or BCC field Outlook will display a list of matching email addresses from the outlook auto-complete cache IE: Email addresses you have already used.

There might be entries that you want to remove, such as entries that are no longer current or accurate. To remove unwanted names, do the following:

  1. Select the unwanted name or email address by using the UP ARROW or DOWN ARROW key.

  2. Click Delete command or press DELETE.

To remove all names from your Auto-Complete list, do the following:

  1. Click the File tab.

  2. Click Options.

  3. Click Mail.

  4. Under Send messages, click Empty Auto-Complete List.