Single instance backup of email message attachments

A system and method for single instance backup. In one embodiment, a method may comprise storing a plurality of duplicate messages on a mail server, where each of the messages includes a copy of an attachment, and storing a copy of each of the plurality of duplicate messages and one or more copies of the attachment to a backup medium, where the number of copies of the attachment stored on the backup medium is less than the number of duplicate messages stored on the backup medium. For example, only a single copy of the attachment may be stored on the backup medium. In one embodiment storing a copy of each of the plurality of duplicate messages and one or more copies of the attachment may comprise extracting metadata from each of the messages, storing the metadata in an attachment index, storing the metadata with each message on the backup medium, and storing the metadata with the copies of the attachment on the backup medium.