A method for downloading an attachment to an attachment viewer of a portable electronic device includes: sending an initial data request from the attachment viewer to a server in response to receipt of an email message including the attachment, building and storing a graph structure within the server representing a map of the attachment, encapsulating the graph structure in data having an attachment viewer readable format and sending an initial chunk of the data to the attachment viewer, the initial chunk of the data being stored on the portable electronic device. The initial chunk of the data is received by the portable electronic device prior to a request to view the attachment being selected by a user.