Server Email Problem

We have recently found that our main shared server IP address is being blocked by many of the anti-spam agencies. We have changed many of the sites to their own dedicated IP addresses, but it still seems that all mail is going via our shared IP address which is still blocked. I need your help in changing the main shared IP address which can be done via WHM/Cpanel and I probably have to update dns with enom, not sure will need your advice, I also need someway of checking for the SPAM to see where its coming from and also to prevent any virus or trojans. This is a relatively small job to test your skills, once completed we would like to keep your details to help with any future problems. Thanks John