what rule I should has for permit access to mail server

["Administrador de Red" <admin@gecyt.cu>]

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




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