To ensure that customer accounts from reseller X do not impact reseller Y and vice versa, we prefer assigning a seperate IP for each reseller. They can add accounts, and they get set up on that particular IP.
One thing we need to continue managing manually however is the /etc/mailips.
I would like for WHM to automatically manage this file so that each domain name - when hosted on IP x - also sends mail from that particular IP address.
With larger server capacity, we are hosting more and more accounts on the same server; IP reputation is important; hence limiting the impact of one problem which causes RBL listing is becoming more important as well.