1. A computer-implemented method for identifying and correlating an incoming electronic mail (e-mail) message to a computing system with an outbound e-mail message previously transmitted by the computing system and referenced in a database stored by the computing system, the method comprising performing computer-implemented operations for: processing outbound e-mail messages from the computing system by identifying data stored in a subject field and an address field of the outbound e-mail messages and storing secure hash values generated from a secret key in the database for the data stored in the subject field and the address field of the outbound e-mail messages; and processing an incoming e-mail message to the computing system by determining whether hash values of data stored in a subject field excluding one or more leading words and an address field of the incoming e-mail message sufficiently match the secure hash values stored in the database for the corresponding subject field and address field of the outbound e-mail messages to correlate the incoming e-mail message with one or more of the outbound e-mail messages, and correlating the incoming e-mail message with one or more of the outbound e-mail messages in response to determining that the hash values of data stored in the subject field excluding one or more leading words and the address field of the incoming e-mail message sufficiently match the secure hash values stored in the database for the corresponding subject field and address field of one or more previously transmitted outbound e-mail messages.