static ip assigning

helo everybody,

from couple of days iam not able to send any mail from my mail server. my all mails are blocked as spam mail. because i don't have any static ip. itseem we installed tata 1 mbps broadband connection with one static ip address. this broadband router connected to linksysys broadband and voice router's internet port. linksys broadband and voice routers ip is 192.168.15.1, 255.255.255.0.from this linksys routers ethernet port we are connecting the internet to the linux firewall's etho(192.168.15.2, 255.255.255.0) port, in this linux server we have two ethernet cards, one for internet and another one eth1 (10.1.0.1, 255.255.255.0)for lan. using port forwarding we are runing this linux firewall. for mail server we r using (linux) fetchmail and sendmail (10.1.0.3 , 255.255.255.0). mail receiving is not a problem for me. within my domail sending mail is ok but only the problem is iam not able to send any mail to other domains like gmail, yahoo, sify.... etc. so please tel me where i need to use the static ip? and how? my static ip is a class A ip with 255.255.255.0 subnet.