what rule I should has for permit access to mail server

Hi Friends.

I need a help very fast.

I has two server linux, the first has some service www,DNS primary, squid and gateway too, the second server is mail server, DNS secondary, then I want to permit access to server mail from my gateway, I write the folowing rules but is´nt working with the Outlook Express.

I can access to internet very well, i test with the ping to www.yahoo.com and the gateway response, but with Outloook Express I can access to mail server, port 25 and port 110.

*nat
:PREROUTING ACCEPT [0:65535]
:POSTROUTING ACCEPT [0:65535]
:OUTPUT ACCEPT [0:65535]
[0:0] -A PREROUTING -i eth0 -p tcp -m tcp --dport 25 -j DNAT --to-destination ip_true:25 [0:0] -A PREROUTING -i eth0 -p tcp -m tcp --dport 110 -j DNAT --to-destination ip_true:110 [0:65535] -A POSTROUTING -o eth0 -j SNAT --to-source ip_gateway_true COMMIT

someone could Help me. please.
thanks very well.

Thomas

Estamos en Calle 20 Numero 4110 % 41 y 47,
Miramar, Playa, Ciudad Habana, Cuba.
Telf:537(203-01-60) y (202-79-20)
Fax: 537(204-96-64)
Visitenos en: http://www.gecyt.cu