Get-PublicFolder -Server SERVERNAME "\" -Recurse -ResultSize:Unlimited | Remove-PublicFolder -Server SERVERNAME -Recurse -ErrorAction:SilentlyContinue 
Get-PublicFolder -Server SERVERNAME "\Non_Ipm_Subtree" -Recurse -ResultSize:Unlimited | Remove-PublicFolder -Server SERVERNAME -Recurse -ErrorAction:SilentlyContinue 

ADSIEDIT PublicFolderDB entfernen

/o=First Organization/ou=Exchange Administrative Group (XXXXXXXXXXX)/cn=Configuration/cn=Servers/cn=SERVERNAME/cn=Microsoft Public MDB
cd %programfiles%\Microsoft\Exchange Server\bin
Setup.com /mode:uninstall