To search for messages, type a word that the messages contain. Note, however, that Search matches "whole words" only—that is, it doesn't recognize partial or similar matches. For example, if you search for benefits, Search won't find benefitor benef. Also, Search doesn't recognize special search characters, such as square brackets, parentheses, currency symbols, ampersands, pound signs, and asterisks.
By default, Search doesn't look in your Trash or Spam folders. To search those folders also, click the down arrow on the right side of the search bar and, in the Search drop-down list, select Mail & Spam & Trash. Learn more about search atusing keyword search to sort messages. Also print out this reference sheet of advanced search operators.