Experimente a opção de confirmação:
Get-CASMailbox -ResultSize unlimited –Filter {(HasActiveSyncDevicePartnership -eq $true) -AND (name -notlike "cas*") -AND (name -notlike "DiscoverysearchMailbox*")} | ForEach {Get-MobileDeviceStatistics -Mailbox $_.Identity | Where-Object {$_.LastSuccessSync -le ((Get-Date).AddDays("-14"))} | Remove-MobileDevice -Confirm:$false}