Gmail Labs has a new characteristic for organizing your messages: Smart Labels. Many people create filters that label messages from mailing lists, newsletters, so Google decided to use false intelligence algorithms to classify messages. Right now, there are only three smart labels: bulk (for newsletters), notifications (for confirmation messages, alerts) and forums (for mailing lists). By default, all the messages labeled as "bulk" are routinely archived, but you can change this setting.
"Smart Labels play nice with other labels and filters too. On the Filters tab under Settings, you'll find that these filters can be edited just like any others. From there, you can also edit your obtainable filters to avoid having them Smart Labeled or change whether mail in a Smart Label skips your inbox," explains Google.
In fact, when you create a filter, Google shows an extra option: category. You can choose from: bulk, forums, notifications, personal, promotions. The first three categories already have matching smart labels and all the messages classified as "promotions" are labeled "bulk". The "personal" group includes the rest of your messages.
Google's classification algorithms aren't perfect, so you may find messages that don't belong to one of three categories, but they're labeled as "notifications" or "bulk". Use the "labels" drop-down to remove the labels that are wrongly added and help Google improve its algorithms.