There might be certain kinds of activity or activity performed by specific users that you really want to know about. Instead of having to remember to search the audit log for those activities, you can use activity alerts to have Office 365 send you an email message when users perform those activities. For example, we can create an activity alert to notify you when a user has been detected as sending suspicious messages outside the organization or sets up email auto-forwarding. The email notification sent to you includes information about which activity was performed and the user who performed it.

Learn more about O365 Activity Alerts: http://bit.ly/2JDuVQD