Search is free-form over all message bodies. Keywords must be four letters or longer; short words are not indexed. You may surround phrases "in quotes" to match the exact phrase, and you can use + and - to require or omit words or phrases. You may also use * to match part of a word. For example: +apples -orang* +"green onions" would match all messages containing apples and green onions, but omit those containing oranges or orangutans.