How can I remove an individual name from a Group on the Autofill feature of Mail? I can remove the individual from the Group in Contacts, but when I use the same Group to create a new email, it keeps adding the removed address anyway!
You've edited the groups in the correct place — Address Book — but there's one more step you need to take. Mail.app reads the core data from Address Book when it starts up. After editing entries in Address Book you'll need to quit and restart Mail.app for any changes to be recognized by Mail.