If you believe that it is an unsolicited email, follow these steps.
1) Open Outlook
2) Select the email that is spam/phishing
3) Click on Mimecast (Make sure that you are signed into Mimecast)
4) Click Report Spam and select the appropriate option
Spam: Unsolicited junk email sent indiscriminately in bulk, often for commercial purposes.
Phishing: The fraudulent practice of sending emails purporting to be from reputable companies in order to induce individuals to reveal personal information, such as passwords and credit card numbers.