Powershell E-Mail Adressen auslesen

$user_extern = @()
$user_intern = @()
$member = @()
$member2 = @()

$user_extern = Get-MsolGroupMember -GroupObjectId (Get-MsolGroup | where DisplayName -EQ ("Verteiler " + $gs)).ObjectId | Select EMailAddress  
$user_intern = Get-MsolGroupMember -GroupObjectId (Get-MsolGroup | where DisplayName -EQ ("Verteiler " + $gs)).ObjectId | Select EMailAddress  

foreach($member in $user_extern){
	foreach($member2 in $user_intern) { 
             Add-MailboxFolderPermission -Identity ($member2+":\Kalender") -User $member -AccessRights PublishingEditor  
        }
}

Fehler beim Aufrufen der Methode, da [System.Management.Automation.PSObject] keine Methode mit dem Namen "op_Addition" enthält.  
In C:\PowerShell\CalendarRights.ps1:24 Zeichen:5
+     ($user_extern[$i] + ":\Kalender")  
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (op_Addition:String) , RuntimeException
    + FullyQualifiedErrorId : MethodNotFound