User Configuration > Administrative Templates > Microsoft Outlook 2016 > Account Settings > Exchange > Offline Address Book
User
HKCU\software\policies\microsoft\exchange\exchange provider
By default, when searching the Offline Address Book, Outlook resolves e-mail addresses using Ambiguous Name Resolution. With Ambiguous Name Resolution, Outlook suggests additional possible matches (if they exist) even if there is a name that matches exactly the e-mail alias entered. By enabling this setting, you can change the behavior so that Outlook returns a single e-mail address if it exactly matches an e-mail alias.