Although PPTP protocol is available on OS X El Captain and earlier or iOS 9 and earlier, it isn’t recommended for use as a private, secure method of communication. This is due to the fact that macOS Sierra and iOS 10 systems have removed PPTP connections from VPN profiles once their device is upgraded. If you have recently set up a PPTP VPN server, macOS Sierra and iOS 10 users will not be able to connect to your server. Remove PPTP VPN before upgrading to macOS Sierra & iOS 10
