User Configuration > Administrative Templates > Microsoft OneNote 2016 > OneNote Options > Send to OneNote
User
HKCU\software\policies\microsoft\office\16.0\onenote\options\outlookandweb
This policy disables the OneNote ''Send to OneNote'' add-in for Microsoft Outlook. By default OneNote installs an add-in on the Outlook toolbar which allows users to send emails to OneNote. The ''Send to OneNote'' button appears on the main mail module in Outlook as well as when viewing an email message. You may disable this feature with this policy.