Either click the zigzag icon next to it, or right-click the specific inbox and select Take "YOUR_ACCOUNT_NAME" Online.
Using Snow Leopard OS. Only the Inbox of my Earthlink mail is not working. It is "grayed" out. I can send, etc. and receive on my computer on my MobileMe address and of course on my iPhone.
I've looked at preferences but don't see anyway to "de-gray" my Inbox?