mail 的韵定

大家新年好!
?大家?忙,我用RedHat6.1砚有一台mail server(ip 202.104.130.66)
DNS server(ip 202.104.130.66)firewall server(?部ip 172.27.122.1
外部ip 202.104.130.67.咀晷是202.104.130.65),我有??咀段(一?是172.27.122.0,咀晷是172.27.122.251,另一?172.16.144.0,咀晷是172.1 6.144.251)?在??是:
172.27.122.0呃一段可以用mail server,而172.16.144.0呃一段不可以用mail server.它能ping 上172.27.122.1,但不能ping 上202.104.130.66.??怎?韵定才能ping 上202.104.130.66,才能用上mail server.因我是菜?,???些.著著