User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Other > Advanced
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\general
This policy setting controls whether e-mail messages dragged from Outlook to the file system are saved in Unicode or ANSI format. If you enable or do not configure this policy setting, when users drag an e-mail message from Outlook to the file system, Outlook uses the Unicode character encoding standard to create the message file, which preserves special characters in the message. If you disable this policy setting, when users drag an e-mail message from Outlook to the file system, the message file created is in ANSI format.