Used when you want to send email to group of people without having to type each individual recipient's name, distribution lists are organized by a particular discussion subject (such as “Marketing”) or by users who share common work that requires them to communicate frequently. Distribution lists are sometimes called distribution groups.
Create a distribution list (group)
Sign in to Office 365 with your work or school account.
Select the app launcher icon and choose Admin.
Choose Groups in the left navigation pane.
Under Type of group, select the dropdown and choose Distribution list.
Enter a name and add a description for your new distribution list.
You can choose whether you want people outside your organization to send email to the distribution list.
When you're ready, click or tap Add to create the distribution list, and Close to view your distribution list.
Check out how to use distribution lists in Outlook 2016 and Outlook on the web in the Use distribution lists in Outlook topic.
Check out Troubleshooting distribution list issues for help with distribution list issues.