We need to add a secondary import feature that will allow us to import a list to an existing Contact List within Email Marketer - however, we need a few new rules:
1. If on the EM Contact List - keep as is
2. If not on the EM Contact List but on import List - Add.
3. If NOT on the Import List - remove from EM Contact List.
Basically we have a customer who needs to import new lists quarterly - but they need to make sure that the Email Marketer (EM) list removes people who are no longer on their list.