Methods for transcoding attachments for mobile devices are described. In some embodiments, attachments associated with any communication are stored on a server. When a communication is sent from a server to a client device, a representation of the attachment that includes an indication of a native file type of the attachment is also sent along with the communication to the client device. In responding to a user's request to view the attachment, the server transcodes the attachment from the attachment's native file type to a viewable file type configured to display in the client device and then transmits at least a portion of the attachment in the viewable file type to the client device for display. Other embodiments are also described.