How to mapping ports from a single public IP to multiple internal servers in Fortigate Firewall?

Solution 1:

Well, it is not possible to forward same port to multiple internal servers over the same public ip. How should the Firewall know which server the request to forward to if requests are coming to the same ip,on the same port?

Your only option is to forward different ports on the firewall, to same ports on the internal servers (example only).

port-3389(Firewall public ip)---->port3389(Server1 private ip)
port-XXXX(Firewall public ip)---->port3389(Server2 private ip)
port-25(Firewall public ip)------>port25(Server3 private ip)

..etc.