Postfix email server config

[NewMee]

Check the gateway address on the Postfix machine, if it's not correct, there cannot be an answer on any other network.

route

Would give something like this:

Kernel IP routing table
Destination     Gateway         Genmask          Flags Metric Ref    Use Iface
192.168.20.0    *                255.255.255.0   U     1      0       0 eth0
default         you.rr.ou.ter    0.0.0.0         UG    0      0       0 eth0

where you.rr.ou.ter should be the address of your gateway.