A secure message that includes an attachment is received at a server. The secure message may have a secure layer that indicates that the secure message is at least digitally signed. The secure message may be provided without the attachment to the mobile device over a wireless network. A request may be received from the mobile device to access the attachment. The request may include an attachment identifier (ID) that identifies the attachment in accordance with a message-attachment indexing system. In response to the request to access the attachment, the server may perform an index lookup to find the attachment based upon the attachment ID, may look through the secure layer of the secure message in order to locate the attachment within the secure message, and may render at least an initial portion of the attachment by the server in a format for viewing by the mobile device.