Blacklisting: This one should be obvious. Blacklisting can occur on both your Act-On mailing domain OR your primary domain. If one of these domains is blacklisted, it will affect the other (assuming they share the same 2nd level domain). You will want to go through the process of delisting as soon this is known. Most blacklists will only process a delist request if you have taking the necessary steps to correct the infraction.