How did your WAN interface become 192.168.1.20 ? The ISP is probably rejecting everything that comes from such an address. Before you spend time messing with mail servers and/or routers, first fix the WAN interface. In most cases, it should be assigned by a DHCP server. In /etc/sysconfig/network-scripts/ifcfg-eth0
, there should be a line like
Start by making sure the ethernet is configured correctly.