This script is used to get the list of all member of a Distribution list that contain other Distribution list, the result is a pure list of user or contact that are contain is those recursive Distribution List I found this useful to manage New-App Userlist with group ex : New-App

Get-DistributionGroupExpandedMember.ps1

Function Get-DistributionGroupExpandedMember { 
    Param( 
            [Parameter(Mandatory=$True,ValueFromPipeline=$True)][String] $Identity 
        ) 
    BEGIN{ 
         
    } 
    PROCESS { 
        $ExpandedDLList = @() 
        [array]$DL = Get-DistributionGroupMember $Identity 
        $tempDLList = @() 
        [array]$tempDLList = Get-DistributionGroupMember $Identity | where {$_.RecipientType -ne "MailUniversalDistributionGroup" -and $_.RecipientType -ne "MailUniversalSecurityGroup"} 
        while(($DL | Where {$_.RecipientType -eq "MailUniversalDistributionGroup"}) -ne $NULL){ 
            foreach($item in ($DL | Where {$_.RecipientType -eq "MailUniversalDistributionGroup" -or $_.RecipientType -ne "MailUniversalSecurityGroup"})){ 
                $DLname = $item.name 
                $DLidentity = $item.identity 
                Write-Verbose "Checking $DLName" 
                if($ExpandedDLList -notcontains $DLidentity){ 
                    Write-Verbose "Expanding $DLname" 
                    $DL = $DL | where {$_.Name -ne $DLname} 
                    $DL += Get-DistributionGroupMember $item.identity 
                    [array]$tempDLList += Get-DistributionGroupMember $item.identity | where {$_.RecipientType -ne "MailUniversalDistributionGroup" -and $_.RecipientType -ne "MailUniversalSecurityGroup"} 
                }else{ 
                    $DL = $DL | where {$_.Name -ne $DLname} 
                } 
                [Array]$ExpandedDLList += $DLidentity 
            } 
        } 
    } 
    END{ 
        return $tempDLList 
    } 
}