netscreen@srx-240# show interfaces 
interface-range interfaces-trust {
    member ge-0/0/4;
    member ge-0/0/5;
    member ge-0/0/6;
    member ge-0/0/7;
    member ge-0/0/8;
    member ge-0/0/9;
    member ge-0/0/10;
    member ge-0/0/11;
    member ge-0/0/12;
    member ge-0/0/13;
    member ge-0/0/14;
    member ge-0/0/15;
    member ge-0/0/2;
    unit 0 {
        family ethernet-switching {
            vlan {
                members vlan-trust;
            }
        }
    }
}
ge-0/0/0 {
    unit 0 {
        family inet {
            address XX.XX.123.194/28 {
                primary;
            }
        }
    }
}
ge-0/0/1 {
    unit 0 {
        family inet;
    }
}
ge-0/0/3 {
    unit 0 {
        family inet;
    }
}
lo0 {
    unit 0 {
        family inet {
            address 127.0.0.1/32;
        }
    }
}
vlan {
    unit 0 {
        family inet {
            address 192.168.2.2/24;
        }
    }
}

NAT:
netscreen@srx-240# show security nat 
source {
    rule-set trust-to-untrust {
        from zone trust;
        to zone untrust;
        rule source-nat-rule {
            match {
                source-address 0.0.0.0/0;
            }
            then {
                source-nat {
                    interface;
                }
            }
        }
    }
}


static {
    rule-set st-mail-dns {
        from zone untrust;
        rule rule1 {
            match {
                destination-address XX.XX.123.195/32;
            }
            then {
                static-nat prefix 192.168.2.20/32;
            }
        }
    }
}
proxy-arp {
    interface ge-0/0/0.0 {
        address {
            XX.XX.123.195/32;
        }
    }
}

netscreen@srx-hqekb# show security policies 
from-zone trust to-zone untrust {
    policy any {
        match {
            source-address any;
            destination-address any;
            application any;
        }
        then {
            permit;
        }
    }
}
from-zone untrust to-zone trust {
    policy st-mail-dns {
        match {
            source-address any;
            destination-address mailsrv;
            application junos-icmp-ping;
        }
        then {
            permit;
        }
    }
}