Returns the membership of all Exchange Online Distribution Groups

GetExchangeGroupMemberships.ps1

$allDistributionGroups = Get-DistributionGroup -ResultSize unlimited
$allGroupMemberships = $allDistributionGroups | ForEach-Object { 
  $thisGroup = $_
  Get-DistributionGroupMember -Identity $thisGroup.Identity | 
    Select-Object `
      @{Name="GroupIdentity";Expression={$thisGroup.primarySmtpAddress}},
      @{Name="MemberAddress";Expression={$_.PrimarySmtpAddress}}
}