MAIL contents won't delete. What does a shadowy folder mean?

I use GMAIL.com email accounts on MAIL. My Mail Activity is out of control. It's constantly running. Even though I delete messages off GMAIL.COM on the internet, I'm being flooded in MAIL with unwanted messages that I cannot delete. Under my MAILBOXES menu are these categories: RSS, ON MY MAC, GMAIL. When I open the GMAIL drop-down, I see a shadowed folder that contains several folders: All, Drafts, Important, Sent, Spam, Starred, Trash. The ALL folder contains 49,716 messages that won't delete. Many of those messages are exact duplicates except for the "time/date" on them. 1) Can I delete the shadowy folder that has become a nightmare to me without affecting my Inbox and normal drafts, sent and trash folders? HELP. I'm getting swallowed up by the MAIL monster.