1. A method for searching e-mails, the method comprising: receiving, at one or more computer systems communicatively coupled to a plurality of databases indexing the e-mails, information indicative of one or more search terms; determining, with one or more processors associated with the one or more computer systems, a query plan based on the one or more search terms that specifies an interleaving between querying a first database in the plurality of databases that contains metadata associated with the e-mails and querying a second database in the plurality of databases that contains a full text index of the e-mails, the interleaving defining how results of a first database query against one database in the first or second databases influence a second database query against the other database in the first or second database; performing, with the one or more processors associated with the one or more computer systems, a search in response to the query plan to determine information related to the one or more e-mails; and generating, with the one or more processors associated with the one or more computer systems, a set of results based on the information related to the one or more e-mails.