When you disable name checking (autoresolution) in Tools, Options, E-mail Options, Advanced E-mail Options, Automatic name checking, Outlook will still resolve the names, but not immediately. You'll need to press Ctrl+K to force autoresolution at any time before sending the message; otherwise Outlook will always resolve the address when you send the message. If a match isn't found, you'll be asked to pick names using the Check Names dialog.