I'm new to act and I can't seem to figure this one out. We have two companies that we share prospects with. I want to create mailing lists to mail promotional mailers to, but I want to make sure that I don't keep mailing to the same people. If I create a mailing list via a lookup and send them a postcard, how would I keep from adding them in future lookups for this same purpose? A better way to say that would be, how do I know if I've sent postcards to them before? I thought about creating groups to remember who I sent cards to, but I don't know how to check for duplicates between 2 or more groups.