Ok, just checked, I use 1.5GB only, but still in modest you're getting only latest 250 messages, so 8GB is not the issue here (check the menu once you click Inbox at the top: Show more (250/xxx) is an option, so you could have 8TB, unless attachments are all loaded). Try with different account? If issue persists something you installed is at fault, if other email works fine make a local copy of the attachment ones and remove them from serv.