[solved] PPTP passthrough

Hi!
Please, help me!
Machines in local network can’t connect to external PPTP VPN server thought Mikrotik NAT.
Which rules I need to add to allow machines with local dynamic dhcp adresses connect to external PPTP servers?

Update:
http://forum.mikrotik.com/t/mikrotik-mikrotik-pptp-problem/51730/1 (good explanation of problem)
http://forum.mikrotik.com/t/feature-request-gre-nat-tracking-pptp/51822/1 (resolution: /ip firewall service-port enable pptp)