I have a Gmail account. For years, it has sync'd very nicely with my Apple Mail folders. Now, several of my Mail folders are no longer syncing with their respective Gmail Label (folder). In some of these folders may show some of the emails stored in my Google Gmail account, but not all. Some other Mail folders are completely empty now despite the fact that their may be 100-150 messages stored in the respective Gmail Label (folder).
I have tried using Apple's "Rebuild" function in Mail, but nothing happens in the Activity window. Any suggestions?
MacBook Air (13-inch, Early 2014), OS X Yosemite (10.10.1), 16 GB Ram; 480 GB SSD