Chapter 10 Install and System Administration for FortiOS 5.0 : PPTP and L2TP : Configuring the FortiGate unit for PPTP VPN
  
Configuring the FortiGate unit for PPTP VPN
To arrange for PPTP packets to pass through the FortiGate unit to an external PPTP server, perform the following tasks in the order given:
Configure user authentication for PPTP clients.
Enable PPTP on the FortiGate unit and specify the range of addresses that can be assigned to PPTP clients when they connect.
Configure PPTP pass through on the FortiGate unit.
See Also
FortiGate unit as a PPTP server
Configuring the FortiGate unit for PPTP pass through
Testing PPTP VPN connections
Logging VPN events
Configuring L2TP VPNs
L2TP configuration overview
Adding the security policy