As far as I know, your Linux machine will only make outbound connections from one of your NICs if it has multiple without bonding/teaming/aggregating, so you will definitely struggle with that on outbound emails if they need to come from each of those 5 IPs. I'm sure with NAT rules you could make the connections come from certain public IPs based on the destination if that's what you are trying to do. I'm with everyone else... Why?
