1. While in your Outlook desktop application, click the File button at the top-left of the window.
2. Click the Options button.
3. Select Mail from the left panel and scroll down to the “Send Messages” section and click Empty Auto-Complete list. When prompted, hit “Yes.”
Note
If you do not wish to utilize the Auto-Complete feature moving forward, uncheck the “Use Auto-Complete List to suggest names when typing in the To, CC, and Bcc lines” before clicking OK.