There are four groups within Office 365 :
- Office 365 Group – Allow to collaborate on files, projects, tasks, and events
- Security Group – Grant access permission at the group level to all the users within the group .
- Mail-Enabled Security Group – Similar to Security Group with the capability to send emails directly to all the member of the group. Both Security groups have access to resources within AD.
- Distribution list – Distribution groups send emails to users at the same time (widely used in exchange server)
“By default only senders within your company can send messages to groups, but you can also allow people outside the organization to send email to groups. For example, email@example.com could be used by anyone and be directed to the internal help desk team.” ref