If you would like to prevent Outlook from auto-completing an address in the To, CC, and BCC lines, this guide will show you step by step.
To access the AutoComplete setting, follow these steps:
Step One: Within the Outlook program, on the File menu, click Options.
Step Two: Select the Mail tab.
Step Three: Scroll approximately halfway down until you see Send messages. Make sure that the Use Auto-Complete List to suggest names when typing in the To, Cc, and Bcc lines box is checked.
