Foreach ($user in $users){

    #All your existing logic and code
    $adUser = Get-ADUser -filter "mail -eq '$($user.email)'" -properties $syncProperties
    foreach ($prop in $syncProperties)
    {
        if ($user.$prop -ne $adUser.$pro)
        {
            Set-ADuser $aduser @{$prop = $user.$prop}
        }
    }
}