Office 365: Disable Cortana briefing emails
Reference
https://docs.microsoft.com/en-us/briefing/be-admin
To unsubscribe <<user@domain.com>> from the Cortana Briefing email:
- Open a new private / incognito window in browser
- Go to https://cortana.office.com/settings?v=unsubscribe
- Log in with the email address that you would like to unsubscribe.