User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Preferences > E-mail Options
User
HKCU\software\policies\microsoft\office\16.0\outlook\preferences
This policy setting controls whether CTRL+ENTER can be used as a shortcut to send an email message. You can change this behavior so that CTRL+ENTER does not send an email message. If you enable this policy setting, you may select one of these choices: - CTRL+Enter is not a shortcut for sending a message - CTRL+Enter is a shortcut for sending a message - CTRL+Enter displays a prompt If you disable or do not configure this policy setting, users can use CTRL+ENTER to send an e-mail message. By default, users are prompted the first time they use the shortcut to confirm sending the message.