Transmitting e-mail over a network. According to a preferred embodiment, a current node in the network receives an e-mail message to be distributed to at least one recipient. The e-mail message comprises an attachment reference comprising the network address of an attachment stored locally to a previous node of the network. The costs of forwarding the e-mail message given a previous network location of the attachment is compared to the costs of moving the attachment locally to the current node. A copy of the attachment is retrieved, stored locally to the current node, and the attachment reference is updated, in accordance with the comparison.