User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Preferences > Junk E-mail
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\mail
This policy setting hides warnings about suspicious domain names in e-mail addresses. If you enable this policy setting, warnings about suspicious domain names in e-mail addresses will be hidden. If you disable or do not configure this policy setting, warnings about suspicious domain names in e-mail addresses will not be hidden.