The "Your daily briefing" email sent from Cortana (cortana@microsoft.com) is delivered to your Dartmouth mailbox by default. The Briefing email helps you stay in control of your calendar and be intentional about your day. Within two hours of your workday (as set up in Outlook), you'll get an email about any relevant items to help you better prepare for the day ahead.
To disable the Briefing email, click the Unsubscribe link at the bottom of the email or at https://cortana.office.com/briefing.
For more information on the Cortana Daily Briefing: https://docs.microsoft.com/en-us/briefing/be-overview.