> It's possible to distribute the sending of mail between the two interfaces?. By example, X domains by interface eth0 and anothers by eth0:1..
This cannot be don with iptables
> I'm looking for an alternative to mi first ip, that's rated as "poor" because of SPAM.
To switch from default ip to secondary You can
iptables -t nat -A OUTPUT -p tcp --dport smtp -j SNAT --to-source new-ip
