Automatically mark or move multiple messages

Labels and filters don't just help you organize where your messages go; they can also make sure that messages fitting certain criteria are handled in a specific way. Want to apply a star to each of the 3000 messages from your mom all at once (she'll love you for it)? Here's the deal:
  1. Open the label (or, your Inbox, or Sent Mail, etc) containing the messages you'd like to select.
  2. Click the Select: All link above your messages.
  3. Click the link that says Select all [number] conversations in [current view].
  4. Select the action you'd like to take from the More Actions... drop-down menu.

That's easy enough for conversations that are already categorized where you want them, but what about the 200 messages scattered throughout your inbox related to that tropical vacation you took last month? No problem. Just create a new filter for them, by following these steps:

  1. Click Create a filter.
  2. Enter your filter criteria, for example, 'subject contains: Hawaii'.
  3. Click Test Search to see which messages match your filter terms. You can update your criteria and run another test search, or click Next Step.
  4. Select one or more actions from the list. (Fun fact: these actions will take place in the order they're listed -- for example, you could choose to Forward matching messages to a specific email address, then Delete the messages).
  5. Presuming you'd like to apply this filter to the messages you already have (rather than only to new messages), select the 'Also apply filter to x conversations below' checkbox.
  6. Click Create Filter.