A method for downloading an attachment to an attachment viewer of a portable electronic device includes: sending an initial data request from said attachment viewer to a server in response to receipt of an email message including said attachment by said portable electronic device; accessing a graph structure representing a map of said attachment from said server, said graph structure having been previously built on said server; reconstructing said graph structure in response to said initial request and encapsulating said graph structure in data having an attachment viewer readable format, said data being stored on said server; and i) downloading successive chunks of said data from said server to said attachment viewer responsive to successive user requests; ii) storing each of said successive chunks of said data on said portable electronic device prior to display thereof; iii) displaying said successive chunks of said data on said portable electronic device and automatically downloading respective next chunks of said data from said server; and iv) while said data chunks of said data remain to be downloaded from said server performing steps i) to iii).