Office 365 - Subscribe or Unsubscribe from a Group?
By default, Group conversations only take place in the Group inbox but if you subscribe to a Group, you will see the conversations and calendar events from the Group sent directly to your personal inbox and calendar. You can also respond to the conversations from the Outlook Desktop App 2016, and your replies are immediately posted to the Group conversation.
If your inbox or calendar becomes inundated with information from the Group, you can always unsubscribe. The conversations will still be available in the Group. There is a convenient unsubscribe link at the bottom of Group email messages.
Unsubscribe: You will still be a part of the group, but you will not receive any conversations or invitations in your personal inbox and calendar.
Leave: You will no longer be a part of the group and you not will be able to access the files or other data.