Just to give you a heads up of a recent change in Office 365 in relation to Groups. Previously when Office 365 Groups were created in Outlook by default they would be set to public meaning anyone in your organisation could see what was happening in your group.
As of the 18th April this has now been changed so that any group created is private by default meaning only approved members are able to see content in the group.
To confirm your organizations setting run the below in PowerShell.
Get-OrganizationConfig | ft DefaultGroupAccessType