Smart mailbox for senders who are not members of a group I want to set up a smart mailbox in Mail that contains messages from any sender who is not a member of a particular group in my address book.

There's an option in the smart mailbox rules for "sender is member of group," but I don't see a way to negate it. Is this possible?
This is maybe a bit counter intuitive but you can do it via the Contacts app.  

You can make an intelligent group in your Contacts app with the criteria: 


is not member in group


and use this group for your smart mailbox.