It would be nice if it was configurable or just automatic that if a customer has a static IP, that IP would be used for sending out e-mail. A common case we see where using just the main IP of the server for delivery is if there is a local spam break out. Say a user's e-mail account gets compromised and it is used to send 10s of thousands of spams. Currently, this results in the entire server getting black listed. If it was configurable, or just 'automatic' for customers with static IPs to have their mail delivered off their IP, then the impact of this kind of thing would be more limited and in particular, customers who pay extra to have a static IP would not be affected by a spam outbreak from one of the domains of the majority of customers who use shared IP. Possibly this is just no doable with Exim?