Hi @Roman Dzichel, MP-Datentechnik GmbH,
If the folder name is "Posteingang Lokal", there may be a typo (you have "Posteingang_LOKAL") in this cmdlet:
Get-MailboxFolderStatistics ******@contoso.com | Where { $_.FolderPath.Contains("Posteingang_LOKAL") } | ft Name, FolderPath
If you still cannot get the folder with this cmdlet, please make sure the folder name is correct and try the following script to see if it works for you:
$path = Get-MailboxFolderstatistics -Identity ******@contoso.com | Where {$_.Name -eq "Posteingang Lokal"} | select-object -ExpandProperty FolderPath
$path = $path -replace '/', '\'
$path
Add-MailboxFolderPermission -Identity ******@contoso.com:$($path) -User ******@contoso.com -AccessRights Editor
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