Smart Mailbox -- Google Folder Doesn't Work

Solution 1:

The solution was in the fact that my Apple ID has been around for a long time and was the same email address as my GMail account. I had to go into Apple's site, manage my ID, and then change my Apple ID to its associated iCloud email address. Then I had to sign out of my Apple ID and back in on my Mac. The confusion within Mail seemed to be rooted in the fact that it couldn't tell the two accounts apart in the filters since they had the same email address even though I could get mail on my iCloud account without issue.