NAT

Sometimes you need your devices (say an SMTP server) to have a specific outbound public IP for things like reverse-DNS look-ups to ensure mail delivery and reputation, or maybe you want traffic from particular devices or policies to go out an IP for means of tracking. It is not immediately obvious on Fortigates how to do this, typically, when you create a policy and NAT traffic out through it, the Fortigate will use its’ own public IP assigned by the ISP to originate the traffic from, if you have got a static IP and use an unnumbered address from your ISP then you might be lucky and your R-DNS might match this, however, in most cases you will have a separate Virtual IP for your SMTP server that is different to this and thus you need the R-DNS lookup to match that of the A-Record....