Kuldeep
A static NAT is bi-directional so it actually means 2 things -
1) the device on the inside with an IP address of 10.150.250.10 will be translated to 10.50.243.243 if it sends packets to a device on the Smtp_DMZ
2) if a device on the Smtp_DMZ sends packets to 10.150.243.243 then the destination IP address will be translated to 10.150.250.10 and sent to the inside device
The static statement is a little confusing to be honest. The logical assumption would be that the IP addresses in the static statement are written in the same order as the interfaces ie.
static (inside,outside) "inside IP address" "outside IP adddress"
but in fact the IP addresses are written in reverse order ie.
static (inside,outside) "outside IP address" "inside IP address"
it's just one of those things you have to get to used to i'm afraid.
Jon