How to Create a Distribution Group

To create a distribution group (mail-enabled group), go to the Office 365 tab and click Mail Enable:

How to create a synchronized Office 365 distribution group using Easy365Manager
Mail enabling the group creates the necessary email attributes in your on-premises Active Directory.

Once the attributes are replicated to Office 365, the Office 365 mail group creation is started.

When the process is completed, you will get access to mail properties like Delegation, Ownership, and Allow External Senders:

Easy365Manager group properties