Gmail Labs update its Offline Gmail to version 0.2. With this update, you can now specify a maximum size for the downloaded attachments. If you don't need to access attachments when you're offline, you can disable the download of attachments. If your running Offline Gmail, and you don’t see the update, just disable and re-enable Gmail offline. And you won't have to download your emails again; you can always choose them not to be removed while disabling Gmail offline, explain Gmail Group.

Source:→ Google System