messaging gateway with two interfaces

HELP ME

I need  implement a scanner that processes outgoing mail, but mail received by an interface with an IP address and send it by another interface with another different IP (like a bridge).
for example
eth0 (outbound mail): 10.2.2.2/24
eth1 (outbound mail to the Internet): 200.3.3.4

this is possible??
currently already set and I can ping from the appliance to the network 10 without problem and also from the appliance to the network 192 but I can not send mail yet.