1. A method of identifying messages on a social networking messaging service, comprising: receiving a search query using a message classification system, where the search query comprises at least one search query term; calculating a plurality of query scores for the search query with respect to a plurality of categories using the message classification system, where: each of the plurality of query scores is a score determined with respect to one of the plurality of categories; a predetermined plurality of keywords is related to each of the plurality of categories; a normalized keyword frequency is assigned to each of the predetermined plurality of keywords related to each of the plurality of categories, where the normalized keyword frequency is determined for a given predetermined keyword from the predetermined plurality of keywords based upon the frequency with which the given predetermined keyword appears within a predetermined training data set comprising a plurality of messages that are relevant to the category to which the given predetermined keyword is related; and calculating a given query score from the plurality of query scores for the search query with respect to a given category from the plurality of categories comprises using the normalized frequencies of the predetermined plurality of keywords related to the given category to determine a likelihood that the at least one search query term is present in a message relevant to the given category; storing the plurality of query scores for the search query with respect to the plurality of categories using the message classification system; identifying at least one category relevant to the search query based on the plurality of stored query scores using the message classification system; retrieving and scoring messages from a social messaging service based upon the search query and the identified at least one category relevant to the search query using the message classification system, where retrieving and scoring messages with respect to the search query and a particular category from the identified at least one category identified as being relevant to the search query using the message classification system comprises: performing a plurality of parallel searches that retrieve messages from a social networking messaging service that match the search query and iterative combinations of the search query and at least one of the predetermined plurality of keywords related to the particular category to retrieve messages likely to be relevant to the particular category using the message classification system; scoring the retrieved messages with respect to the search query and the particular category using the message classification system by: calculating a sum using the normalized frequencies of the predetermined plurality of keywords related to the particular category using the message classification system, where the sum is determined based at least in part upon the normalized frequencies of the predetermined plurality of keywords related to the particular category present in the retrieved message; calculating a ratio of search query terms in the retrieved message to the total number of search query terms using the message classification system; scoring the retrieved messages based upon the calculated sum and the calculated ratio using the message classification system; and storing the retrieved message scores using the message classification system; returning at least one of the retrieved messages as the search result based at least in part on the retrieved message scores using the message classification system.